diff --git a/libcxx/include/__configuration/platform.h b/libcxx/include/__configuration/platform.h
index 8d0f8f63f521..f3c199dee172 100644
--- a/libcxx/include/__configuration/platform.h
+++ b/libcxx/include/__configuration/platform.h
@@ -42,6 +42,13 @@
 #  endif
 #endif
 
+// This is required in order for _NEWLIB_VERSION to be defined in places where we use it.
+// TODO: We shouldn't be including arbitrarily-named headers from libc++ since this can break valid
+//       user code. Move code paths that need _NEWLIB_VERSION to another customization mechanism.
+#if __has_include(<picolibc.h>)
+#  include <picolibc.h>
+#endif
+
 #ifndef __BYTE_ORDER__
 #  error                                                                                                               \
       "Your compiler doesn't seem to define __BYTE_ORDER__, which is required by libc++ to know the endianness of your target platform"
diff --git a/libcxx/include/__locale b/libcxx/include/__locale
index dfe79d5e506f..93187dc1d0d9 100644
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -11,6 +11,9 @@
 #define _LIBCPP___LOCALE
 
 #include <__config>
+
+#if _LIBCPP_HAS_LOCALIZATION
+
 #include <__locale_dir/locale_base_api.h>
 #include <__memory/shared_count.h>
 #include <__mutex/once_flag.h>
@@ -24,18 +27,18 @@
 #include <string>
 
 // Some platforms require more includes than others. Keep the includes on all plaforms for now.
-#include <cstddef>
-#include <cstring>
+#  include <cstddef>
+#  include <cstring>
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-#  include <cwchar>
-#else
-#  include <__std_mbstate_t.h>
-#endif
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    include <cwchar>
+#  else
+#    include <__std_mbstate_t.h>
+#  endif
 
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
+#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#    pragma GCC system_header
+#  endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -85,9 +88,9 @@ public:
   // locale operations:
   string name() const;
   bool operator==(const locale&) const;
-#if _LIBCPP_STD_VER <= 17
+#  if _LIBCPP_STD_VER <= 17
   _LIBCPP_HIDE_FROM_ABI bool operator!=(const locale& __y) const { return !(*this == __y); }
-#endif
+#  endif
   template <class _CharT, class _Traits, class _Allocator>
   _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS bool
   operator()(const basic_string<_CharT, _Traits, _Allocator>&, const basic_string<_CharT, _Traits, _Allocator>&) const;
@@ -237,9 +240,9 @@ long collate<_CharT>::do_hash(const char_type* __lo, const char_type* __hi) cons
 }
 
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<char>;
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<wchar_t>;
-#endif
+#  endif
 
 // template <class CharT> class collate_byname;
 
@@ -264,7 +267,7 @@ protected:
   string_type do_transform(const char_type* __lo, const char_type* __hi) const override;
 };
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI collate_byname<wchar_t> : public collate<wchar_t> {
   __locale::__locale_t __l_;
@@ -283,7 +286,7 @@ protected:
       const char_type* __lo1, const char_type* __hi1, const char_type* __lo2, const char_type* __hi2) const override;
   string_type do_transform(const char_type* __lo, const char_type* __hi) const override;
 };
-#endif
+#  endif
 
 template <class _CharT, class _Traits, class _Allocator>
 bool locale::operator()(const basic_string<_CharT, _Traits, _Allocator>& __x,
@@ -296,7 +299,7 @@ bool locale::operator()(const basic_string<_CharT, _Traits, _Allocator>& __x,
 
 class _LIBCPP_EXPORTED_FROM_ABI ctype_base {
 public:
-#if defined(_LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE)
+#  if defined(_LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE)
   typedef unsigned long mask;
   static const mask space  = 1 << 0;
   static const mask print  = 1 << 1;
@@ -308,14 +311,14 @@ public:
   static const mask punct  = 1 << 7;
   static const mask xdigit = 1 << 8;
   static const mask blank  = 1 << 9;
-#  if defined(__BIONIC__)
+#    if defined(__BIONIC__)
   // Historically this was a part of regex_traits rather than ctype_base. The
   // historical value of the constant is preserved for ABI compatibility.
   static const mask __regex_word = 0x8000;
-#  else
+#    else
   static const mask __regex_word = 1 << 10;
-#  endif // defined(__BIONIC__)
-#elif defined(__GLIBC__)
+#    endif // defined(__BIONIC__)
+#  elif defined(__GLIBC__)
   typedef unsigned short mask;
   static const mask space  = _ISspace;
   static const mask print  = _ISprint;
@@ -327,12 +330,12 @@ public:
   static const mask punct  = _ISpunct;
   static const mask xdigit = _ISxdigit;
   static const mask blank  = _ISblank;
-#  if defined(__mips__) || (BYTE_ORDER == BIG_ENDIAN)
+#    if defined(__mips__) || (BYTE_ORDER == BIG_ENDIAN)
   static const mask __regex_word = static_cast<mask>(_ISbit(15));
-#  else
+#    else
   static const mask __regex_word = 0x80;
-#  endif
-#elif defined(_LIBCPP_MSVCRT_LIKE)
+#    endif
+#  elif defined(_LIBCPP_MSVCRT_LIKE)
   typedef unsigned short mask;
   static const mask space        = _SPACE;
   static const mask print        = _BLANK | _PUNCT | _ALPHA | _DIGIT;
@@ -345,16 +348,16 @@ public:
   static const mask xdigit       = _HEX;
   static const mask blank        = _BLANK;
   static const mask __regex_word = 0x4000; // 0x8000 and 0x0100 and 0x00ff are used
-#  define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
-#  define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
-#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__)
-#  ifdef __APPLE__
+#    define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
+#    define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
+#  elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__)
+#    ifdef __APPLE__
   typedef uint32_t mask;
-#  elif defined(__FreeBSD__)
+#    elif defined(__FreeBSD__)
   typedef unsigned long mask;
-#  elif defined(__NetBSD__)
+#    elif defined(__NetBSD__)
   typedef unsigned short mask;
-#  endif
+#    endif
   static const mask space  = _CTYPE_S;
   static const mask print  = _CTYPE_R;
   static const mask cntrl  = _CTYPE_C;
@@ -365,16 +368,16 @@ public:
   static const mask punct  = _CTYPE_P;
   static const mask xdigit = _CTYPE_X;
 
-#  if defined(__NetBSD__)
+#    if defined(__NetBSD__)
   static const mask blank = _CTYPE_BL;
   // NetBSD defines classes up to 0x2000
   // see sys/ctype_bits.h, _CTYPE_Q
   static const mask __regex_word = 0x8000;
-#  else
+#    else
   static const mask blank        = _CTYPE_B;
   static const mask __regex_word = 0x80;
-#  endif
-#elif defined(_AIX)
+#    endif
+#  elif defined(_AIX)
   typedef unsigned int mask;
   static const mask space        = _ISSPACE;
   static const mask print        = _ISPRINT;
@@ -387,7 +390,7 @@ public:
   static const mask xdigit       = _ISXDIGIT;
   static const mask blank        = _ISBLANK;
   static const mask __regex_word = 0x8000;
-#elif defined(_NEWLIB_VERSION)
+#  elif defined(_NEWLIB_VERSION)
   // Same type as Newlib's _ctype_ array in newlib/libc/include/ctype.h.
   typedef char mask;
   // In case char is signed, static_cast is needed to avoid warning on
@@ -404,11 +407,11 @@ public:
   static const mask blank  = static_cast<mask>(_B);
   // mask is already fully saturated, use a different type in regex_type_traits.
   static const unsigned short __regex_word = 0x100;
-#  define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
-#  define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
-#  define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_XDIGIT
-#elif defined(__MVS__)
-#  if defined(__NATIVE_ASCII_F)
+#    define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
+#    define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
+#    define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_XDIGIT
+#  elif defined(__MVS__)
+#    if defined(__NATIVE_ASCII_F)
   typedef unsigned int mask;
   static const mask space  = _ISSPACE_A;
   static const mask print  = _ISPRINT_A;
@@ -420,7 +423,7 @@ public:
   static const mask punct  = _ISPUNCT_A;
   static const mask xdigit = _ISXDIGIT_A;
   static const mask blank  = _ISBLANK_A;
-#  else
+#    else
   typedef unsigned short mask;
   static const mask space  = __ISSPACE;
   static const mask print  = __ISPRINT;
@@ -432,11 +435,11 @@ public:
   static const mask punct  = __ISPUNCT;
   static const mask xdigit = __ISXDIGIT;
   static const mask blank  = __ISBLANK;
-#  endif
+#    endif
   static const mask __regex_word = 0x8000;
-#else
-#  error unknown rune table for this platform -- do you mean to define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE?
-#endif
+#  else
+#    error unknown rune table for this platform -- do you mean to define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE?
+#  endif
   static const mask alnum = alpha | digit;
   static const mask graph = alnum | punct;
 
@@ -450,7 +453,7 @@ public:
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS ctype;
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI ctype<wchar_t> : public locale::facet, public ctype_base {
 public:
@@ -515,7 +518,7 @@ protected:
   virtual const char_type*
   do_narrow(const char_type* __low, const char_type* __high, char __dfault, char* __dest) const;
 };
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 inline _LIBCPP_HIDE_FROM_ABI bool __libcpp_isascii(int __c) { return (__c & ~0x7F) == 0; }
 
@@ -580,25 +583,25 @@ public:
 
   static locale::id id;
 
-#ifdef _CACHED_RUNES
+#  ifdef _CACHED_RUNES
   static const size_t table_size = _CACHED_RUNES;
-#else
+#  else
   static const size_t table_size = 256; // FIXME: Don't hardcode this.
-#endif
+#  endif
   _LIBCPP_HIDE_FROM_ABI const mask* table() const _NOEXCEPT { return __tab_; }
   static const mask* classic_table() _NOEXCEPT;
-#if defined(__GLIBC__) || defined(__EMSCRIPTEN__)
+#  if defined(__GLIBC__) || defined(__EMSCRIPTEN__)
   static const int* __classic_upper_table() _NOEXCEPT;
   static const int* __classic_lower_table() _NOEXCEPT;
-#endif
-#if defined(__NetBSD__)
+#  endif
+#  if defined(__NetBSD__)
   static const short* __classic_upper_table() _NOEXCEPT;
   static const short* __classic_lower_table() _NOEXCEPT;
-#endif
-#if defined(__MVS__)
+#  endif
+#  if defined(__MVS__)
   static const unsigned short* __classic_upper_table() _NOEXCEPT;
   static const unsigned short* __classic_lower_table() _NOEXCEPT;
-#endif
+#  endif
 
 protected:
   ~ctype() override;
@@ -633,7 +636,7 @@ protected:
   const char_type* do_tolower(char_type* __low, const char_type* __high) const override;
 };
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI ctype_byname<wchar_t> : public ctype<wchar_t> {
   __locale::__locale_t __l_;
@@ -658,7 +661,7 @@ protected:
   const char_type*
   do_narrow(const char_type* __low, const char_type* __high, char __dfault, char* __dest) const override;
 };
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 template <class _CharT>
 inline _LIBCPP_HIDE_FROM_ABI bool isspace(_CharT __c, const locale& __loc) {
@@ -824,7 +827,7 @@ protected:
 
 // template <> class codecvt<wchar_t, char, mbstate_t>
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI codecvt<wchar_t, char, mbstate_t> : public locale::facet, public codecvt_base {
   __locale::__locale_t __l_;
@@ -903,7 +906,7 @@ protected:
   virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const;
   virtual int do_max_length() const _NOEXCEPT;
 };
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 // template <> class codecvt<char16_t, char, mbstate_t> // deprecated in C++20
 
@@ -985,7 +988,7 @@ protected:
   virtual int do_max_length() const _NOEXCEPT;
 };
 
-#if _LIBCPP_HAS_CHAR8_T
+#  if _LIBCPP_HAS_CHAR8_T
 
 // template <> class codecvt<char16_t, char8_t, mbstate_t> // C++20
 
@@ -1066,7 +1069,7 @@ protected:
   virtual int do_max_length() const _NOEXCEPT;
 };
 
-#endif
+#  endif
 
 // template <> class codecvt<char32_t, char, mbstate_t> // deprecated in C++20
 
@@ -1148,7 +1151,7 @@ protected:
   virtual int do_max_length() const _NOEXCEPT;
 };
 
-#if _LIBCPP_HAS_CHAR8_T
+#  if _LIBCPP_HAS_CHAR8_T
 
 // template <> class codecvt<char32_t, char8_t, mbstate_t> // C++20
 
@@ -1229,7 +1232,7 @@ protected:
   virtual int do_max_length() const _NOEXCEPT;
 };
 
-#endif
+#  endif
 
 // template <class _InternT, class _ExternT, class _StateT> class codecvt_byname
 
@@ -1251,17 +1254,17 @@ codecvt_byname<_InternT, _ExternT, _StateT>::~codecvt_byname() {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char, char, mbstate_t>;
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<wchar_t, char, mbstate_t>;
-#endif
+#  endif
 extern template class _LIBCPP_DEPRECATED_IN_CXX20
 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char, mbstate_t>; // deprecated in C++20
 extern template class _LIBCPP_DEPRECATED_IN_CXX20
 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char, mbstate_t>; // deprecated in C++20
-#if _LIBCPP_HAS_CHAR8_T
+#  if _LIBCPP_HAS_CHAR8_T
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char8_t, mbstate_t>; // C++20
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char8_t, mbstate_t>; // C++20
-#endif
+#  endif
 
 template <size_t _Np>
 struct __narrow_to_utf8 {
@@ -1441,7 +1444,7 @@ protected:
   string __grouping_;
 };
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI numpunct<wchar_t> : public locale::facet {
 public:
@@ -1470,7 +1473,7 @@ protected:
   char_type __thousands_sep_;
   string __grouping_;
 };
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 // template <class charT> class numpunct_byname
 
@@ -1493,7 +1496,7 @@ private:
   void __init(const char*);
 };
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI numpunct_byname<wchar_t> : public numpunct<wchar_t> {
 public:
@@ -1509,8 +1512,10 @@ protected:
 private:
   void __init(const char*);
 };
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 _LIBCPP_END_NAMESPACE_STD
 
+#endif // _LIBCPP_HAS_LOCALIZATION
+
 #endif // _LIBCPP___LOCALE
diff --git a/libcxx/include/__locale_dir/locale_base_api.h b/libcxx/include/__locale_dir/locale_base_api.h
index c1e73caeecce..9d92a5ea1f0a 100644
--- a/libcxx/include/__locale_dir/locale_base_api.h
+++ b/libcxx/include/__locale_dir/locale_base_api.h
@@ -111,57 +111,59 @@
 //  int     __sscanf(const char*, __locale_t, const char*, ...);     // required by the headers
 // }
 
-#if defined(__APPLE__)
-#  include <__locale_dir/support/apple.h>
-#elif defined(__FreeBSD__)
-#  include <__locale_dir/support/freebsd.h>
-#elif defined(_LIBCPP_MSVCRT_LIKE)
-#  include <__locale_dir/support/windows.h>
-#elif defined(__Fuchsia__)
-#  include <__locale_dir/support/fuchsia.h>
-#else
+#if _LIBCPP_HAS_LOCALIZATION
+
+#  if defined(__APPLE__)
+#    include <__locale_dir/support/apple.h>
+#  elif defined(__FreeBSD__)
+#    include <__locale_dir/support/freebsd.h>
+#  elif defined(_LIBCPP_MSVCRT_LIKE)
+#    include <__locale_dir/support/windows.h>
+#  elif defined(__Fuchsia__)
+#    include <__locale_dir/support/fuchsia.h>
+#  else
 
 // TODO: This is a temporary definition to bridge between the old way we defined the locale base API
 //       (by providing global non-reserved names) and the new API. As we move individual platforms
 //       towards the new way of defining the locale base API, this should disappear since each platform
 //       will define those directly.
-#  if defined(_AIX) || defined(__MVS__)
-#    include <__locale_dir/locale_base_api/ibm.h>
-#  elif defined(__ANDROID__)
-#    include <__locale_dir/locale_base_api/android.h>
-#  elif defined(__OpenBSD__)
-#    include <__locale_dir/locale_base_api/openbsd.h>
-#  elif defined(__wasi__) || _LIBCPP_HAS_MUSL_LIBC
-#    include <__locale_dir/locale_base_api/musl.h>
-#  endif
+#    if defined(_AIX) || defined(__MVS__)
+#      include <__locale_dir/locale_base_api/ibm.h>
+#    elif defined(__ANDROID__)
+#      include <__locale_dir/locale_base_api/android.h>
+#    elif defined(__OpenBSD__)
+#      include <__locale_dir/locale_base_api/openbsd.h>
+#    elif defined(__wasi__) || _LIBCPP_HAS_MUSL_LIBC
+#      include <__locale_dir/locale_base_api/musl.h>
+#    endif
 
-#  include <__locale_dir/locale_base_api/bsd_locale_fallbacks.h>
+#    include <__locale_dir/locale_base_api/bsd_locale_fallbacks.h>
 
-#  include <__cstddef/size_t.h>
-#  include <__utility/forward.h>
-#  include <ctype.h>
-#  include <string.h>
-#  include <time.h>
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
-#    include <wctype.h>
-#  endif
+#    include <__cstddef/size_t.h>
+#    include <__utility/forward.h>
+#    include <ctype.h>
+#    include <string.h>
+#    include <time.h>
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
+#      include <wctype.h>
+#    endif
 _LIBCPP_BEGIN_NAMESPACE_STD
 namespace __locale {
 //
 // Locale management
 //
-#  define _LIBCPP_COLLATE_MASK LC_COLLATE_MASK
-#  define _LIBCPP_CTYPE_MASK LC_CTYPE_MASK
-#  define _LIBCPP_MONETARY_MASK LC_MONETARY_MASK
-#  define _LIBCPP_NUMERIC_MASK LC_NUMERIC_MASK
-#  define _LIBCPP_TIME_MASK LC_TIME_MASK
-#  define _LIBCPP_MESSAGES_MASK LC_MESSAGES_MASK
-#  define _LIBCPP_ALL_MASK LC_ALL_MASK
-#  define _LIBCPP_LC_ALL LC_ALL
+#    define _LIBCPP_COLLATE_MASK LC_COLLATE_MASK
+#    define _LIBCPP_CTYPE_MASK LC_CTYPE_MASK
+#    define _LIBCPP_MONETARY_MASK LC_MONETARY_MASK
+#    define _LIBCPP_NUMERIC_MASK LC_NUMERIC_MASK
+#    define _LIBCPP_TIME_MASK LC_TIME_MASK
+#    define _LIBCPP_MESSAGES_MASK LC_MESSAGES_MASK
+#    define _LIBCPP_ALL_MASK LC_ALL_MASK
+#    define _LIBCPP_LC_ALL LC_ALL
 
 using __locale_t _LIBCPP_NODEBUG = locale_t;
 
-#  if defined(_LIBCPP_BUILDING_LIBRARY)
+#    if defined(_LIBCPP_BUILDING_LIBRARY)
 using __lconv_t _LIBCPP_NODEBUG = lconv;
 
 inline _LIBCPP_HIDE_FROM_ABI __locale_t __newlocale(int __category_mask, const char* __name, __locale_t __loc) {
@@ -175,7 +177,7 @@ inline _LIBCPP_HIDE_FROM_ABI char* __setlocale(int __category, char const* __loc
 inline _LIBCPP_HIDE_FROM_ABI void __freelocale(__locale_t __loc) { freelocale(__loc); }
 
 inline _LIBCPP_HIDE_FROM_ABI __lconv_t* __localeconv(__locale_t& __loc) { return __libcpp_localeconv_l(__loc); }
-#  endif // _LIBCPP_BUILDING_LIBRARY
+#    endif // _LIBCPP_BUILDING_LIBRARY
 
 //
 // Strtonum functions
@@ -204,15 +206,15 @@ __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
 //
 // Character manipulation functions
 //
-#  if defined(_LIBCPP_BUILDING_LIBRARY)
+#    if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __islower(int __ch, __locale_t __loc) { return islower_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI int __isupper(int __ch, __locale_t __loc) { return isupper_l(__ch, __loc); }
-#  endif
+#    endif
 
 inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __ch, __locale_t __loc) { return isdigit_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __ch, __locale_t __loc) { return isxdigit_l(__ch, __loc); }
 
-#  if defined(_LIBCPP_BUILDING_LIBRARY)
+#    if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __strcoll(const char* __s1, const char* __s2, __locale_t __loc) {
   return strcoll_l(__s1, __s2, __loc);
 }
@@ -222,7 +224,7 @@ inline _LIBCPP_HIDE_FROM_ABI size_t __strxfrm(char* __dest, const char* __src, s
 inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __ch, __locale_t __loc) { return toupper_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI int __tolower(int __ch, __locale_t __loc) { return tolower_l(__ch, __loc); }
 
-#    if _LIBCPP_HAS_WIDE_CHARACTERS
+#      if _LIBCPP_HAS_WIDE_CHARACTERS
 inline _LIBCPP_HIDE_FROM_ABI int __wcscoll(const wchar_t* __s1, const wchar_t* __s2, __locale_t __loc) {
   return wcscoll_l(__s1, __s2, __loc);
 }
@@ -244,7 +246,7 @@ inline _LIBCPP_HIDE_FROM_ABI int __iswpunct(wint_t __ch, __locale_t __loc) { ret
 inline _LIBCPP_HIDE_FROM_ABI int __iswxdigit(wint_t __ch, __locale_t __loc) { return iswxdigit_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI wint_t __towupper(wint_t __ch, __locale_t __loc) { return towupper_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI wint_t __towlower(wint_t __ch, __locale_t __loc) { return towlower_l(__ch, __loc); }
-#    endif
+#      endif
 
 inline _LIBCPP_HIDE_FROM_ABI size_t
 __strftime(char* __s, size_t __max, const char* __format, const tm* __tm, __locale_t __loc) {
@@ -257,7 +259,7 @@ __strftime(char* __s, size_t __max, const char* __format, const tm* __tm, __loca
 inline _LIBCPP_HIDE_FROM_ABI decltype(__libcpp_mb_cur_max_l(__locale_t())) __mb_len_max(__locale_t __loc) {
   return __libcpp_mb_cur_max_l(__loc);
 }
-#    if _LIBCPP_HAS_WIDE_CHARACTERS
+#      if _LIBCPP_HAS_WIDE_CHARACTERS
 inline _LIBCPP_HIDE_FROM_ABI wint_t __btowc(int __ch, __locale_t __loc) { return __libcpp_btowc_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI int __wctob(wint_t __ch, __locale_t __loc) { return __libcpp_wctob_l(__ch, __loc); }
 inline _LIBCPP_HIDE_FROM_ABI size_t
@@ -285,17 +287,17 @@ inline _LIBCPP_HIDE_FROM_ABI size_t
 __mbsrtowcs(wchar_t* __dest, const char** __src, size_t __len, mbstate_t* __ps, __locale_t __loc) {
   return __libcpp_mbsrtowcs_l(__dest, __src, __len, __ps, __loc);
 }
-#    endif // _LIBCPP_HAS_WIDE_CHARACTERS
-#  endif   // _LIBCPP_BUILDING_LIBRARY
+#      endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#    endif   // _LIBCPP_BUILDING_LIBRARY
 
 _LIBCPP_DIAGNOSTIC_PUSH
 _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wgcc-compat")
 _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wformat-nonliteral") // GCC doesn't support [[gnu::format]] on variadic templates
-#  ifdef _LIBCPP_COMPILER_CLANG_BASED
-#    define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) _LIBCPP_ATTRIBUTE_FORMAT(__VA_ARGS__)
-#  else
-#    define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) /* nothing */
-#  endif
+#    ifdef _LIBCPP_COMPILER_CLANG_BASED
+#      define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) _LIBCPP_ATTRIBUTE_FORMAT(__VA_ARGS__)
+#    else
+#      define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) /* nothing */
+#    endif
 
 template <class... _Args>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(__printf__, 4, 5) int __snprintf(
@@ -313,11 +315,13 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(__scanf__, 3, 4) int __s
   return std::__libcpp_sscanf_l(__s, __loc, __format, std::forward<_Args>(__args)...);
 }
 _LIBCPP_DIAGNOSTIC_POP
-#  undef _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT
+#    undef _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT
 
 } // namespace __locale
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // Compatibility definition of locale base APIs
+#  endif // Compatibility definition of locale base APIs
+
+#endif // _LIBCPP_HAS_LOCALIZATION
 
 #endif // _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_H
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
index de5c07035dba..9a35f7ab9701 100644
--- a/libcxx/include/fstream
+++ b/libcxx/include/fstream
@@ -189,35 +189,36 @@ typedef basic_fstream<wchar_t> wfstream;
 #if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 #  include <__cxx03/fstream>
 #else
-#  include <__algorithm/max.h>
-#  include <__assert>
 #  include <__config>
-#  include <__filesystem/path.h>
-#  include <__fwd/fstream.h>
-#  include <__locale>
-#  include <__memory/addressof.h>
-#  include <__memory/unique_ptr.h>
-#  include <__ostream/basic_ostream.h>
-#  include <__type_traits/enable_if.h>
-#  include <__type_traits/is_same.h>
-#  include <__utility/move.h>
-#  include <__utility/swap.h>
-#  include <__utility/unreachable.h>
-#  include <cstdio>
-#  include <istream>
-#  include <streambuf>
-#  include <typeinfo>
-#  include <version>
-
-#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#    pragma GCC system_header
-#  endif
-
-_LIBCPP_PUSH_MACROS
-#  include <__undef_macros>
 
 #  if _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION
 
+#    include <__algorithm/max.h>
+#    include <__assert>
+#    include <__filesystem/path.h>
+#    include <__fwd/fstream.h>
+#    include <__locale>
+#    include <__memory/addressof.h>
+#    include <__memory/unique_ptr.h>
+#    include <__ostream/basic_ostream.h>
+#    include <__type_traits/enable_if.h>
+#    include <__type_traits/is_same.h>
+#    include <__utility/move.h>
+#    include <__utility/swap.h>
+#    include <__utility/unreachable.h>
+#    include <cstdio>
+#    include <istream>
+#    include <streambuf>
+#    include <typeinfo>
+#    include <version>
+
+#    if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#      pragma GCC system_header
+#    endif
+
+_LIBCPP_PUSH_MACROS
+#    include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #    if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_WIN32API)
@@ -1570,10 +1571,10 @@ extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_filebuf<char>;
 
 _LIBCPP_END_NAMESPACE_STD
 
-#  endif // _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION
-
 _LIBCPP_POP_MACROS
 
+#  endif // _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION
+
 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #    include <atomic>
 #    include <concepts>
diff --git a/libcxx/include/regex b/libcxx/include/regex
index dcee77cfacc3..cfcbc2c6b21f 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -792,48 +792,50 @@ typedef regex_token_iterator<wstring::const_iterator> wsregex_token_iterator;
 #if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 #  include <__cxx03/regex>
 #else
-#  include <__algorithm/find.h>
-#  include <__algorithm/search.h>
-#  include <__assert>
 #  include <__config>
-#  include <__iterator/back_insert_iterator.h>
-#  include <__iterator/default_sentinel.h>
-#  include <__iterator/wrap_iter.h>
-#  include <__locale>
-#  include <__memory/shared_ptr.h>
-#  include <__memory_resource/polymorphic_allocator.h>
-#  include <__type_traits/is_swappable.h>
-#  include <__utility/move.h>
-#  include <__utility/pair.h>
-#  include <__utility/swap.h>
-#  include <__verbose_abort>
-#  include <deque>
-#  include <stdexcept>
-#  include <string>
-#  include <vector>
-#  include <version>
+
+#  if _LIBCPP_HAS_LOCALIZATION
+
+#    include <__algorithm/find.h>
+#    include <__algorithm/search.h>
+#    include <__iterator/back_insert_iterator.h>
+#    include <__iterator/default_sentinel.h>
+#    include <__iterator/wrap_iter.h>
+#    include <__locale>
+#    include <__memory/shared_ptr.h>
+#    include <__memory_resource/polymorphic_allocator.h>
+#    include <__type_traits/is_swappable.h>
+#    include <__utility/move.h>
+#    include <__utility/pair.h>
+#    include <__utility/swap.h>
+#    include <__verbose_abort>
+#    include <deque>
+#    include <stdexcept>
+#    include <string>
+#    include <vector>
+#    include <version>
 
 // standard-mandated includes
 
 // [iterator.range]
-#  include <__iterator/access.h>
-#  include <__iterator/data.h>
-#  include <__iterator/empty.h>
-#  include <__iterator/reverse_access.h>
-#  include <__iterator/size.h>
+#    include <__iterator/access.h>
+#    include <__iterator/data.h>
+#    include <__iterator/empty.h>
+#    include <__iterator/reverse_access.h>
+#    include <__iterator/size.h>
 
 // [re.syn]
-#  include <compare>
-#  include <initializer_list>
+#    include <compare>
+#    include <initializer_list>
 
-#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#    pragma GCC system_header
-#  endif
+#    if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#      pragma GCC system_header
+#    endif
 
 _LIBCPP_PUSH_MACROS
-#  include <__undef_macros>
+#    include <__undef_macros>
 
-#  define _LIBCPP_REGEX_COMPLEXITY_FACTOR 4096
+#    define _LIBCPP_REGEX_COMPLEXITY_FACTOR 4096
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -846,11 +848,11 @@ enum syntax_option_type {
   nosubs   = 1 << 1,
   optimize = 1 << 2,
   collate  = 1 << 3,
-#  ifdef _LIBCPP_ABI_REGEX_CONSTANTS_NONZERO
+#    ifdef _LIBCPP_ABI_REGEX_CONSTANTS_NONZERO
   ECMAScript = 1 << 9,
-#  else
+#    else
   ECMAScript = 0,
-#  endif
+#    endif
   basic    = 1 << 4,
   extended = 1 << 5,
   awk      = 1 << 6,
@@ -861,11 +863,11 @@ enum syntax_option_type {
 };
 
 _LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR syntax_option_type __get_grammar(syntax_option_type __g) {
-#  ifdef _LIBCPP_ABI_REGEX_CONSTANTS_NONZERO
+#    ifdef _LIBCPP_ABI_REGEX_CONSTANTS_NONZERO
   return static_cast<syntax_option_type>(__g & 0x3F0);
-#  else
+#    else
   return static_cast<syntax_option_type>(__g & 0x1F0);
-#  endif
+#    endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR syntax_option_type operator~(syntax_option_type __x) {
@@ -987,11 +989,11 @@ public:
 
 template <regex_constants::error_type _Ev>
 [[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI void __throw_regex_error() {
-#  if _LIBCPP_HAS_EXCEPTIONS
+#    if _LIBCPP_HAS_EXCEPTIONS
   throw regex_error(_Ev);
-#  else
+#    else
   _LIBCPP_VERBOSE_ABORT("regex_error was thrown in -fno-exceptions mode");
-#  endif
+#    endif
 }
 
 template <class _CharT>
@@ -1000,7 +1002,7 @@ public:
   typedef _CharT char_type;
   typedef basic_string<char_type> string_type;
   typedef locale locale_type;
-#  if defined(__BIONIC__) || defined(_NEWLIB_VERSION)
+#    if defined(__BIONIC__) || defined(_NEWLIB_VERSION)
   // Originally bionic's ctype_base used its own ctype masks because the
   // builtin ctype implementation wasn't in libc++ yet. Bionic's ctype mask
   // was only 8 bits wide and already saturated, so it used a wider type here
@@ -1015,9 +1017,9 @@ public:
   // often used for space constrained environments, so it makes sense not to
   // duplicate the ctype table.
   typedef uint16_t char_class_type;
-#  else
+#    else
   typedef ctype_base::mask char_class_type;
-#  endif
+#    endif
 
   static const char_class_type __regex_word = ctype_base::__regex_word;
 
@@ -1057,30 +1059,30 @@ private:
 
   template <class _ForwardIterator>
   string_type __transform_primary(_ForwardIterator __f, _ForwardIterator __l, char) const;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
   template <class _ForwardIterator>
   string_type __transform_primary(_ForwardIterator __f, _ForwardIterator __l, wchar_t) const;
-#  endif
+#    endif
   template <class _ForwardIterator>
   string_type __lookup_collatename(_ForwardIterator __f, _ForwardIterator __l, char) const;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
   template <class _ForwardIterator>
   string_type __lookup_collatename(_ForwardIterator __f, _ForwardIterator __l, wchar_t) const;
-#  endif
+#    endif
   template <class _ForwardIterator>
   char_class_type __lookup_classname(_ForwardIterator __f, _ForwardIterator __l, bool __icase, char) const;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
   template <class _ForwardIterator>
   char_class_type __lookup_classname(_ForwardIterator __f, _ForwardIterator __l, bool __icase, wchar_t) const;
-#  endif
+#    endif
 
   static int __regex_traits_value(unsigned char __ch, int __radix);
   _LIBCPP_HIDE_FROM_ABI int __regex_traits_value(char __ch, int __radix) const {
     return __regex_traits_value(static_cast<unsigned char>(__ch), __radix);
   }
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
   _LIBCPP_HIDE_FROM_ABI int __regex_traits_value(wchar_t __ch, int __radix) const;
-#  endif
+#    endif
 };
 
 template <class _CharT>
@@ -1139,7 +1141,7 @@ regex_traits<_CharT>::__transform_primary(_ForwardIterator __f, _ForwardIterator
   return __d;
 }
 
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 template <class _CharT>
 template <class _ForwardIterator>
 typename regex_traits<_CharT>::string_type
@@ -1158,7 +1160,7 @@ regex_traits<_CharT>::__transform_primary(_ForwardIterator __f, _ForwardIterator
   }
   return __d;
 }
-#  endif
+#    endif
 
 // lookup_collatename is very FreeBSD-specific
 
@@ -1183,7 +1185,7 @@ regex_traits<_CharT>::__lookup_collatename(_ForwardIterator __f, _ForwardIterato
   return __r;
 }
 
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 template <class _CharT>
 template <class _ForwardIterator>
 typename regex_traits<_CharT>::string_type
@@ -1211,7 +1213,7 @@ regex_traits<_CharT>::__lookup_collatename(_ForwardIterator __f, _ForwardIterato
   }
   return __r;
 }
-#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#    endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 // lookup_classname
 
@@ -1226,7 +1228,7 @@ regex_traits<_CharT>::__lookup_classname(_ForwardIterator __f, _ForwardIterator
   return std::__get_classname(__s.c_str(), __icase);
 }
 
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 template <class _CharT>
 template <class _ForwardIterator>
 typename regex_traits<_CharT>::char_class_type
@@ -1242,7 +1244,7 @@ regex_traits<_CharT>::__lookup_classname(_ForwardIterator __f, _ForwardIterator
   }
   return __get_classname(__n.c_str(), __icase);
 }
-#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#    endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 template <class _CharT>
 bool regex_traits<_CharT>::isctype(char_type __c, char_class_type __m) const {
@@ -1253,28 +1255,28 @@ bool regex_traits<_CharT>::isctype(char_type __c, char_class_type __m) const {
 
 inline _LIBCPP_HIDE_FROM_ABI bool __is_07(unsigned char __c) {
   return (__c & 0xF8u) ==
-#  if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+#    if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
          0xF0;
-#  else
+#    else
          0x30;
-#  endif
+#    endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI bool __is_89(unsigned char __c) {
   return (__c & 0xFEu) ==
-#  if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+#    if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
          0xF8;
-#  else
+#    else
          0x38;
-#  endif
+#    endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI unsigned char __to_lower(unsigned char __c) {
-#  if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+#    if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
   return __c & 0xBF;
-#  else
+#    else
   return __c | 0x20;
-#  endif
+#    endif
 }
 
 template <class _CharT>
@@ -1293,12 +1295,12 @@ int regex_traits<_CharT>::__regex_traits_value(unsigned char __ch, int __radix)
   return -1;
 }
 
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 template <class _CharT>
 inline int regex_traits<_CharT>::__regex_traits_value(wchar_t __ch, int __radix) const {
   return __regex_traits_value(static_cast<unsigned char>(__ct_->narrow(__ch, char_type())), __radix);
 }
-#  endif
+#    endif
 
 template <class _CharT>
 class __node;
@@ -1941,10 +1943,10 @@ public:
 
 template <>
 _LIBCPP_EXPORTED_FROM_ABI void __match_any_but_newline<char>::__exec(__state&) const;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 _LIBCPP_EXPORTED_FROM_ABI void __match_any_but_newline<wchar_t>::__exec(__state&) const;
-#  endif
+#    endif
 
 // __match_char
 
@@ -2265,13 +2267,13 @@ template <class _CharT, class _Traits = regex_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_regex;
 
 typedef basic_regex<char> regex;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 typedef basic_regex<wchar_t> wregex;
-#  endif
+#    endif
 
 template <class _CharT, class _Traits>
-class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(regex)
-    _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wregex)) basic_regex {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(regex) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wregex))
+    basic_regex {
 public:
   // types:
   typedef _CharT value_type;
@@ -2338,21 +2340,21 @@ public:
       : __flags_(__f), __marked_count_(0), __loop_count_(0), __open_count_(0), __end_(nullptr) {
     __init(__first, __last);
   }
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI basic_regex(initializer_list<value_type> __il, flag_type __f = regex_constants::ECMAScript)
       : __flags_(__f), __marked_count_(0), __loop_count_(0), __open_count_(0), __end_(nullptr) {
     __init(__il.begin(), __il.end());
   }
-#  endif // _LIBCPP_CXX03_LANG
+#    endif // _LIBCPP_CXX03_LANG
 
   //    ~basic_regex() = default;
 
   //     basic_regex& operator=(const basic_regex&) = default;
   //     basic_regex& operator=(basic_regex&&) = default;
   _LIBCPP_HIDE_FROM_ABI basic_regex& operator=(const value_type* __p) { return assign(__p); }
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI basic_regex& operator=(initializer_list<value_type> __il) { return assign(__il); }
-#  endif // _LIBCPP_CXX03_LANG
+#    endif // _LIBCPP_CXX03_LANG
   template <class _ST, class _SA>
   _LIBCPP_HIDE_FROM_ABI basic_regex& operator=(const basic_string<value_type, _ST, _SA>& __p) {
     return assign(__p);
@@ -2360,9 +2362,9 @@ public:
 
   // assign:
   _LIBCPP_HIDE_FROM_ABI basic_regex& assign(const basic_regex& __that) { return *this = __that; }
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI basic_regex& assign(basic_regex&& __that) _NOEXCEPT { return *this = std::move(__that); }
-#  endif
+#    endif
   _LIBCPP_HIDE_FROM_ABI basic_regex& assign(const value_type* __p, flag_type __f = regex_constants::ECMAScript) {
     return assign(__p, __p + __traits_.length(__p), __f);
   }
@@ -2399,14 +2401,14 @@ public:
     return assign(basic_regex(__first, __last, __f));
   }
 
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
 
   _LIBCPP_HIDE_FROM_ABI basic_regex&
   assign(initializer_list<value_type> __il, flag_type __f = regex_constants::ECMAScript) {
     return assign(__il.begin(), __il.end(), __f);
   }
 
-#  endif // _LIBCPP_CXX03_LANG
+#    endif // _LIBCPP_CXX03_LANG
 
   // const operations:
   _LIBCPP_HIDE_FROM_ABI unsigned mark_count() const { return __marked_count_; }
@@ -2647,11 +2649,11 @@ private:
   friend class __lookahead;
 };
 
-#  if _LIBCPP_STD_VER >= 17
+#    if _LIBCPP_STD_VER >= 17
 template <class _ForwardIterator, __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> = 0>
 basic_regex(_ForwardIterator, _ForwardIterator, regex_constants::syntax_option_type = regex_constants::ECMAScript)
     -> basic_regex<typename iterator_traits<_ForwardIterator>::value_type>;
-#  endif
+#    endif
 
 template <class _CharT, class _Traits>
 const regex_constants::syntax_option_type basic_regex<_CharT, _Traits>::icase;
@@ -4184,10 +4186,10 @@ void basic_regex<_CharT, _Traits>::__push_lookahead(const basic_regex& __exp, bo
 
 typedef sub_match<const char*> csub_match;
 typedef sub_match<string::const_iterator> ssub_match;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 typedef sub_match<const wchar_t*> wcsub_match;
 typedef sub_match<wstring::const_iterator> wssub_match;
-#  endif
+#    endif
 
 template <class _BidirectionalIterator>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(csub_match)
@@ -4227,7 +4229,7 @@ inline _LIBCPP_HIDE_FROM_ABI bool operator==(const sub_match<_BiIter>& __x, cons
   return __x.compare(__y) == 0;
 }
 
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 using __sub_match_cat _LIBCPP_NODEBUG =
     compare_three_way_result_t<basic_string<typename iterator_traits<_BiIter>::value_type>>;
@@ -4236,7 +4238,7 @@ template <class _BiIter>
 _LIBCPP_HIDE_FROM_ABI auto operator<=>(const sub_match<_BiIter>& __x, const sub_match<_BiIter>& __y) {
   return static_cast<__sub_match_cat<_BiIter>>(__x.compare(__y) <=> 0);
 }
-#  else  // _LIBCPP_STD_VER >= 20
+#    else  // _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const sub_match<_BiIter>& __x, const sub_match<_BiIter>& __y) {
   return !(__x == __y);
@@ -4303,7 +4305,7 @@ operator<=(const basic_string<typename iterator_traits<_BiIter>::value_type, _ST
            const sub_match<_BiIter>& __y) {
   return !(__y < __x);
 }
-#  endif // _LIBCPP_STD_VER >= 20
+#    endif // _LIBCPP_STD_VER >= 20
 
 template <class _BiIter, class _ST, class _SA>
 inline _LIBCPP_HIDE_FROM_ABI bool
@@ -4312,7 +4314,7 @@ operator==(const sub_match<_BiIter>& __x,
   return __x.compare(typename sub_match<_BiIter>::string_type(__y.data(), __y.size())) == 0;
 }
 
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
 template <class _BiIter, class _ST, class _SA>
 _LIBCPP_HIDE_FROM_ABI auto
 operator<=>(const sub_match<_BiIter>& __x,
@@ -4320,7 +4322,7 @@ operator<=>(const sub_match<_BiIter>& __x,
   return static_cast<__sub_match_cat<_BiIter>>(
       __x.compare(typename sub_match<_BiIter>::string_type(__y.data(), __y.size())) <=> 0);
 }
-#  else  // _LIBCPP_STD_VER >= 20
+#    else  // _LIBCPP_STD_VER >= 20
 template <class _BiIter, class _ST, class _SA>
 inline _LIBCPP_HIDE_FROM_ABI bool
 operator!=(const sub_match<_BiIter>& __x,
@@ -4391,7 +4393,7 @@ inline _LIBCPP_HIDE_FROM_ABI bool
 operator<=(typename iterator_traits<_BiIter>::value_type const* __x, const sub_match<_BiIter>& __y) {
   return !(__y < __x);
 }
-#  endif // _LIBCPP_STD_VER >= 20
+#    endif // _LIBCPP_STD_VER >= 20
 
 template <class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI bool
@@ -4399,13 +4401,13 @@ operator==(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::val
   return __x.compare(__y) == 0;
 }
 
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 _LIBCPP_HIDE_FROM_ABI auto
 operator<=>(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::value_type const* __y) {
   return static_cast<__sub_match_cat<_BiIter>>(__x.compare(__y) <=> 0);
 }
-#  else  // _LIBCPP_STD_VER >= 20
+#    else  // _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI bool
 operator!=(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::value_type const* __y) {
@@ -4473,7 +4475,7 @@ inline _LIBCPP_HIDE_FROM_ABI bool
 operator<=(typename iterator_traits<_BiIter>::value_type const& __x, const sub_match<_BiIter>& __y) {
   return !(__y < __x);
 }
-#  endif // _LIBCPP_STD_VER >= 20
+#    endif // _LIBCPP_STD_VER >= 20
 
 template <class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI bool
@@ -4482,14 +4484,14 @@ operator==(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::val
   return __x.compare(string_type(1, __y)) == 0;
 }
 
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 _LIBCPP_HIDE_FROM_ABI auto
 operator<=>(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::value_type const& __y) {
   using string_type = basic_string<typename iterator_traits<_BiIter>::value_type>;
   return static_cast<__sub_match_cat<_BiIter>>(__x.compare(string_type(1, __y)) <=> 0);
 }
-#  else  // _LIBCPP_STD_VER >= 20
+#    else  // _LIBCPP_STD_VER >= 20
 template <class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI bool
 operator!=(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::value_type const& __y) {
@@ -4520,7 +4522,7 @@ inline _LIBCPP_HIDE_FROM_ABI bool
 operator<=(const sub_match<_BiIter>& __x, typename iterator_traits<_BiIter>::value_type const& __y) {
   return !(__y < __x);
 }
-#  endif // _LIBCPP_STD_VER >= 20
+#    endif // _LIBCPP_STD_VER >= 20
 
 template <class _CharT, class _ST, class _BiIter>
 inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _ST>&
@@ -4530,10 +4532,10 @@ operator<<(basic_ostream<_CharT, _ST>& __os, const sub_match<_BiIter>& __m) {
 
 typedef match_results<const char*> cmatch;
 typedef match_results<string::const_iterator> smatch;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 typedef match_results<const wchar_t*> wcmatch;
 typedef match_results<wstring::const_iterator> wsmatch;
-#  endif
+#    endif
 
 template <class _BidirectionalIterator, class _Allocator>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(cmatch) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wcmatch))
@@ -4563,12 +4565,12 @@ public:
   typedef basic_string<char_type> string_type;
 
   // construct/copy/destroy:
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
   match_results() : match_results(allocator_type()) {}
   explicit match_results(const allocator_type& __a);
-#  else
+#    else
   explicit match_results(const allocator_type& __a = allocator_type());
-#  endif
+#    endif
 
   //    match_results(const match_results&) = default;
   //    match_results& operator=(const match_results&) = default;
@@ -4818,13 +4820,13 @@ _LIBCPP_HIDE_FROM_ABI bool operator==(const match_results<_BidirectionalIterator
   return __x.__matches_ == __y.__matches_ && __x.__prefix_ == __y.__prefix_ && __x.__suffix_ == __y.__suffix_;
 }
 
-#  if _LIBCPP_STD_VER < 20
+#    if _LIBCPP_STD_VER < 20
 template <class _BidirectionalIterator, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const match_results<_BidirectionalIterator, _Allocator>& __x,
                                              const match_results<_BidirectionalIterator, _Allocator>& __y) {
   return !(__x == __y);
 }
-#  endif
+#    endif
 
 template <class _BidirectionalIterator, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI void
@@ -5236,13 +5238,13 @@ regex_search(const basic_string<_CharT, _ST, _SA>& __s,
   return __r;
 }
 
-#  if _LIBCPP_STD_VER >= 14
+#    if _LIBCPP_STD_VER >= 14
 template <class _ST, class _SA, class _Ap, class _Cp, class _Tp>
 bool regex_search(const basic_string<_Cp, _ST, _SA>&& __s,
                   match_results<typename basic_string<_Cp, _ST, _SA>::const_iterator, _Ap>&,
                   const basic_regex<_Cp, _Tp>& __e,
                   regex_constants::match_flag_type __flags = regex_constants::match_default) = delete;
-#  endif
+#    endif
 
 // regex_match
 
@@ -5291,14 +5293,14 @@ regex_match(const basic_string<_CharT, _ST, _SA>& __s,
   return std::regex_match(__s.begin(), __s.end(), __m, __e, __flags);
 }
 
-#  if _LIBCPP_STD_VER >= 14
+#    if _LIBCPP_STD_VER >= 14
 template <class _ST, class _SA, class _Allocator, class _CharT, class _Traits>
 inline _LIBCPP_HIDE_FROM_ABI bool
 regex_match(const basic_string<_CharT, _ST, _SA>&& __s,
             match_results<typename basic_string<_CharT, _ST, _SA>::const_iterator, _Allocator>& __m,
             const basic_regex<_CharT, _Traits>& __e,
             regex_constants::match_flag_type __flags = regex_constants::match_default) = delete;
-#  endif
+#    endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_HIDE_FROM_ABI bool
@@ -5325,10 +5327,10 @@ class _LIBCPP_TEMPLATE_VIS regex_iterator;
 
 typedef regex_iterator<const char*> cregex_iterator;
 typedef regex_iterator<string::const_iterator> sregex_iterator;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 typedef regex_iterator<const wchar_t*> wcregex_iterator;
 typedef regex_iterator<wstring::const_iterator> wsregex_iterator;
-#  endif
+#    endif
 
 template <class _BidirectionalIterator, class _CharT, class _Traits>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(cregex_iterator)
@@ -5341,9 +5343,9 @@ public:
   typedef const value_type* pointer;
   typedef const value_type& reference;
   typedef forward_iterator_tag iterator_category;
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
   typedef input_iterator_tag iterator_concept;
-#  endif
+#    endif
 
 private:
   _BidirectionalIterator __begin_;
@@ -5358,20 +5360,20 @@ public:
                  _BidirectionalIterator __b,
                  const regex_type& __re,
                  regex_constants::match_flag_type __m = regex_constants::match_default);
-#  if _LIBCPP_STD_VER >= 14
+#    if _LIBCPP_STD_VER >= 14
   regex_iterator(_BidirectionalIterator __a,
                  _BidirectionalIterator __b,
                  const regex_type&& __re,
                  regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
-#  endif
+#    endif
 
   _LIBCPP_HIDE_FROM_ABI bool operator==(const regex_iterator& __x) const;
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
   _LIBCPP_HIDE_FROM_ABI bool operator==(default_sentinel_t) const { return *this == regex_iterator(); }
-#  endif
-#  if _LIBCPP_STD_VER < 20
+#    endif
+#    if _LIBCPP_STD_VER < 20
   _LIBCPP_HIDE_FROM_ABI bool operator!=(const regex_iterator& __x) const { return !(*this == __x); }
-#  endif
+#    endif
 
   _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __match_; }
   _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return std::addressof(__match_); }
@@ -5455,10 +5457,10 @@ class _LIBCPP_TEMPLATE_VIS regex_token_iterator;
 
 typedef regex_token_iterator<const char*> cregex_token_iterator;
 typedef regex_token_iterator<string::const_iterator> sregex_token_iterator;
-#  if _LIBCPP_HAS_WIDE_CHARACTERS
+#    if _LIBCPP_HAS_WIDE_CHARACTERS
 typedef regex_token_iterator<const wchar_t*> wcregex_token_iterator;
 typedef regex_token_iterator<wstring::const_iterator> wsregex_token_iterator;
-#  endif
+#    endif
 
 template <class _BidirectionalIterator, class _CharT, class _Traits>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_PREFERRED_NAME(cregex_token_iterator)
@@ -5472,9 +5474,9 @@ public:
   typedef const value_type* pointer;
   typedef const value_type& reference;
   typedef forward_iterator_tag iterator_category;
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
   typedef input_iterator_tag iterator_concept;
-#  endif
+#    endif
 
 private:
   typedef regex_iterator<_BidirectionalIterator, _CharT, _Traits> _Position;
@@ -5492,67 +5494,67 @@ public:
                        const regex_type& __re,
                        int __submatch                       = 0,
                        regex_constants::match_flag_type __m = regex_constants::match_default);
-#  if _LIBCPP_STD_VER >= 14
+#    if _LIBCPP_STD_VER >= 14
   regex_token_iterator(_BidirectionalIterator __a,
                        _BidirectionalIterator __b,
                        const regex_type&& __re,
                        int __submatch                       = 0,
                        regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
-#  endif
+#    endif
 
   regex_token_iterator(_BidirectionalIterator __a,
                        _BidirectionalIterator __b,
                        const regex_type& __re,
                        const vector<int>& __submatches,
                        regex_constants::match_flag_type __m = regex_constants::match_default);
-#  if _LIBCPP_STD_VER >= 14
-  regex_token_iterator(_BidirectionalIterator __a,
-                       _BidirectionalIterator __b,
-                       const regex_type&& __re,
-                       const vector<int>& __submatches,
-                       regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
-#  endif
-
-#  ifndef _LIBCPP_CXX03_LANG
-  regex_token_iterator(_BidirectionalIterator __a,
-                       _BidirectionalIterator __b,
-                       const regex_type& __re,
-                       initializer_list<int> __submatches,
-                       regex_constants::match_flag_type __m = regex_constants::match_default);
-
 #    if _LIBCPP_STD_VER >= 14
   regex_token_iterator(_BidirectionalIterator __a,
                        _BidirectionalIterator __b,
                        const regex_type&& __re,
-                       initializer_list<int> __submatches,
+                       const vector<int>& __submatches,
                        regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
 #    endif
-#  endif // _LIBCPP_CXX03_LANG
+
+#    ifndef _LIBCPP_CXX03_LANG
+  regex_token_iterator(_BidirectionalIterator __a,
+                       _BidirectionalIterator __b,
+                       const regex_type& __re,
+                       initializer_list<int> __submatches,
+                       regex_constants::match_flag_type __m = regex_constants::match_default);
+
+#      if _LIBCPP_STD_VER >= 14
+  regex_token_iterator(_BidirectionalIterator __a,
+                       _BidirectionalIterator __b,
+                       const regex_type&& __re,
+                       initializer_list<int> __submatches,
+                       regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
+#      endif
+#    endif // _LIBCPP_CXX03_LANG
   template <size_t _Np>
   regex_token_iterator(_BidirectionalIterator __a,
                        _BidirectionalIterator __b,
                        const regex_type& __re,
                        const int (&__submatches)[_Np],
                        regex_constants::match_flag_type __m = regex_constants::match_default);
-#  if _LIBCPP_STD_VER >= 14
+#    if _LIBCPP_STD_VER >= 14
   template <size_t _Np>
   regex_token_iterator(_BidirectionalIterator __a,
                        _BidirectionalIterator __b,
                        const regex_type&& __re,
                        const int (&__submatches)[_Np],
                        regex_constants::match_flag_type __m = regex_constants::match_default) = delete;
-#  endif
+#    endif
 
   regex_token_iterator(const regex_token_iterator&);
   regex_token_iterator& operator=(const regex_token_iterator&);
 
   _LIBCPP_HIDE_FROM_ABI bool operator==(const regex_token_iterator& __x) const;
-#  if _LIBCPP_STD_VER >= 20
+#    if _LIBCPP_STD_VER >= 20
   _LIBCPP_HIDE_FROM_ABI bool operator==(default_sentinel_t) const { return *this == regex_token_iterator(); }
-#  endif
-#  if _LIBCPP_STD_VER < 20
+#    endif
+#    if _LIBCPP_STD_VER < 20
   _LIBCPP_HIDE_FROM_ABI bool operator!=(const regex_token_iterator& __x) const { return !(*this == __x); }
-#  endif
+#    endif
 
   _LIBCPP_HIDE_FROM_ABI const value_type& operator*() const { return *__result_; }
   _LIBCPP_HIDE_FROM_ABI const value_type* operator->() const { return __result_; }
@@ -5614,7 +5616,7 @@ regex_token_iterator<_BidirectionalIterator, _CharT, _Traits>::regex_token_itera
   __init(__a, __b);
 }
 
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
 
 template <class _BidirectionalIterator, class _CharT, class _Traits>
 regex_token_iterator<_BidirectionalIterator, _CharT, _Traits>::regex_token_iterator(
@@ -5627,7 +5629,7 @@ regex_token_iterator<_BidirectionalIterator, _CharT, _Traits>::regex_token_itera
   __init(__a, __b);
 }
 
-#  endif // _LIBCPP_CXX03_LANG
+#    endif // _LIBCPP_CXX03_LANG
 
 template <class _BidirectionalIterator, class _CharT, class _Traits>
 template <size_t _Np>
@@ -5802,7 +5804,7 @@ regex_replace(const _CharT* __s,
 
 _LIBCPP_END_NAMESPACE_STD
 
-#  if _LIBCPP_STD_VER >= 17
+#    if _LIBCPP_STD_VER >= 17
 _LIBCPP_BEGIN_NAMESPACE_STD
 namespace pmr {
 template <class _BidirT>
@@ -5812,16 +5814,18 @@ using match_results _LIBCPP_AVAILABILITY_PMR =
 using cmatch _LIBCPP_AVAILABILITY_PMR = match_results<const char*>;
 using smatch _LIBCPP_AVAILABILITY_PMR = match_results<std::pmr::string::const_iterator>;
 
-#    if _LIBCPP_HAS_WIDE_CHARACTERS
+#      if _LIBCPP_HAS_WIDE_CHARACTERS
 using wcmatch _LIBCPP_AVAILABILITY_PMR = match_results<const wchar_t*>;
 using wsmatch _LIBCPP_AVAILABILITY_PMR = match_results<std::pmr::wstring::const_iterator>;
-#    endif
+#      endif
 } // namespace pmr
 _LIBCPP_END_NAMESPACE_STD
-#  endif
+#    endif
 
 _LIBCPP_POP_MACROS
 
+#  endif // _LIBCPP_HAS_LOCALIZATION
+
 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #    include <atomic>
 #    include <concepts>
diff --git a/libcxx/include/strstream b/libcxx/include/strstream
index 90d56694e7a6..1a17f8389c07 100644
--- a/libcxx/include/strstream
+++ b/libcxx/include/strstream
@@ -133,30 +133,33 @@ private:
 #  include <__cxx03/strstream>
 #else
 #  include <__config>
-#  include <__ostream/basic_ostream.h>
-#  include <istream>
-#  include <streambuf>
-#  include <version>
 
-#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#    pragma GCC system_header
-#  endif
+#  if _LIBCPP_HAS_LOCALIZATION
 
-#  if _LIBCPP_STD_VER < 26 || defined(_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM) || defined(_LIBCPP_BUILDING_LIBRARY)
+#    include <__ostream/basic_ostream.h>
+#    include <istream>
+#    include <streambuf>
+#    include <version>
+
+#    if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#      pragma GCC system_header
+#    endif
+
+#    if _LIBCPP_STD_VER < 26 || defined(_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM) || defined(_LIBCPP_BUILDING_LIBRARY)
 
 _LIBCPP_PUSH_MACROS
-#    include <__undef_macros>
+#      include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 class _LIBCPP_DEPRECATED _LIBCPP_EXPORTED_FROM_ABI strstreambuf : public streambuf {
 public:
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI strstreambuf() : strstreambuf(0) {}
   explicit strstreambuf(streamsize __alsize);
-#    else
+#      else
   explicit strstreambuf(streamsize __alsize = 0);
-#    endif
+#      endif
   strstreambuf(void* (*__palloc)(size_t), void (*__pfree)(void*));
   strstreambuf(char* __gnext, streamsize __n, char* __pbeg = nullptr);
   strstreambuf(const char* __gnext, streamsize __n);
@@ -166,10 +169,10 @@ public:
   strstreambuf(unsigned char* __gnext, streamsize __n, unsigned char* __pbeg = nullptr);
   strstreambuf(const unsigned char* __gnext, streamsize __n);
 
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI strstreambuf(strstreambuf&& __rhs);
   _LIBCPP_HIDE_FROM_ABI strstreambuf& operator=(strstreambuf&& __rhs);
-#    endif // _LIBCPP_CXX03_LANG
+#      endif // _LIBCPP_CXX03_LANG
 
   ~strstreambuf() override;
 
@@ -203,7 +206,7 @@ private:
   void __init(char* __gnext, streamsize __n, char* __pbeg);
 };
 
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
 
 inline _LIBCPP_HIDE_FROM_ABI strstreambuf::strstreambuf(strstreambuf&& __rhs)
     : streambuf(__rhs),
@@ -232,7 +235,7 @@ inline _LIBCPP_HIDE_FROM_ABI strstreambuf& strstreambuf::operator=(strstreambuf&
   return *this;
 }
 
-#    endif // _LIBCPP_CXX03_LANG
+#      endif // _LIBCPP_CXX03_LANG
 
 class _LIBCPP_DEPRECATED _LIBCPP_EXPORTED_FROM_ABI istrstream : public istream {
 public:
@@ -241,7 +244,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI istrstream(const char* __s, streamsize __n) : istream(&__sb_), __sb_(__s, __n) {}
   _LIBCPP_HIDE_FROM_ABI istrstream(char* __s, streamsize __n) : istream(&__sb_), __sb_(__s, __n) {}
 
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI istrstream(istrstream&& __rhs) // extension
       : istream(std::move(static_cast<istream&>(__rhs))), __sb_(std::move(__rhs.__sb_)) {
     istream::set_rdbuf(&__sb_);
@@ -252,7 +255,7 @@ public:
     istream::operator=(std::move(__rhs));
     return *this;
   }
-#    endif // _LIBCPP_CXX03_LANG
+#      endif // _LIBCPP_CXX03_LANG
 
   ~istrstream() override;
 
@@ -274,7 +277,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI ostrstream(char* __s, int __n, ios_base::openmode __mode = ios_base::out)
       : ostream(&__sb_), __sb_(__s, __n, __s + (__mode & ios::app ? std::strlen(__s) : 0)) {}
 
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI ostrstream(ostrstream&& __rhs) // extension
       : ostream(std::move(static_cast<ostream&>(__rhs))), __sb_(std::move(__rhs.__sb_)) {
     ostream::set_rdbuf(&__sb_);
@@ -285,7 +288,7 @@ public:
     ostream::operator=(std::move(__rhs));
     return *this;
   }
-#    endif // _LIBCPP_CXX03_LANG
+#      endif // _LIBCPP_CXX03_LANG
 
   ~ostrstream() override;
 
@@ -316,7 +319,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI strstream(char* __s, int __n, ios_base::openmode __mode = ios_base::in | ios_base::out)
       : iostream(&__sb_), __sb_(__s, __n, __s + (__mode & ios::app ? std::strlen(__s) : 0)) {}
 
-#    ifndef _LIBCPP_CXX03_LANG
+#      ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI strstream(strstream&& __rhs) // extension
       : iostream(std::move(static_cast<iostream&>(__rhs))), __sb_(std::move(__rhs.__sb_)) {
     iostream::set_rdbuf(&__sb_);
@@ -327,7 +330,7 @@ public:
     iostream::operator=(std::move(__rhs));
     return *this;
   }
-#    endif // _LIBCPP_CXX03_LANG
+#      endif // _LIBCPP_CXX03_LANG
 
   ~strstream() override;
 
@@ -350,7 +353,11 @@ _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
-#  endif // _LIBCPP_STD_VER < 26 || defined(_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM) || defined(_LIBCPP_BUILDING_LIBRARY)
-#endif   // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
+#    endif // _LIBCPP_STD_VER < 26 || defined(_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM) ||
+           // defined(_LIBCPP_BUILDING_LIBRARY)
+
+#  endif // _LIBCPP_HAS_LOCALIZATION
+
+#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_STRSTREAM
diff --git a/libcxx/test/configs/armv7m-picolibc-libc++.cfg.in b/libcxx/test/configs/armv7m-picolibc-libc++.cfg.in
index 7aedfde89916..9bff5021494e 100644
--- a/libcxx/test/configs/armv7m-picolibc-libc++.cfg.in
+++ b/libcxx/test/configs/armv7m-picolibc-libc++.cfg.in
@@ -11,10 +11,6 @@ config.substitutions.append(('%{compile_flags}',
     # "large atomic operation may incur significant performance penalty; the
     # access size (4 bytes) exceeds the max lock-free size (0 bytes)"
     ' -Wno-atomic-alignment'
-
-    # Various libc++ headers check for the definition of _NEWLIB_VERSION
-    # which for picolibc is defined in picolibc.h.
-    ' -include picolibc.h'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib -nostdlib++ -L %{lib-dir} -lc++ -lc++abi'
diff --git a/libcxx/test/libcxx/system_reserved_names.gen.py b/libcxx/test/libcxx/system_reserved_names.gen.py
index f01126249c88..244af4bd1f38 100644
--- a/libcxx/test/libcxx/system_reserved_names.gen.py
+++ b/libcxx/test/libcxx/system_reserved_names.gen.py
@@ -11,6 +11,7 @@
 # provided macros (in other words, ensure that we push/pop correctly everywhere).
 
 # RUN: %{python} %s %{libcxx-dir}/utils
+# END.
 
 import sys
 
@@ -28,6 +29,11 @@ for header in public_headers:
 {lit_header_restrictions.get(header, '')}
 {lit_header_undeprecations.get(header, '')}
 
+// UNSUPPORTED: FROZEN-CXX03-HEADERS-FIXME
+
+// This is required to detect the platform we're building for below.
+#include <__config>
+
 #define SYSTEM_RESERVED_NAME This name should not be used in libc++
 
 // libc++ does not use single-letter names as a matter of principle.