[flang-rt] Avoid duplicate definition of std::__libcpp_verbose_abort (#175551)

If a project depends on the Flang runtime and on libc++, linking fails
because `std::__libcpp_verbose_abort` is defined in both libraries.

Avoid that duplicate definition by defining `_LIBCPP_VERBOSE_ABORT`
before including any C++ headers and by renaming that symbol in the
Flang runtime to `flang_rt_verbose_abort`.

The function that is modified was originally introduced in D158957 to
solve an undefined symbol error when linking pure-Fortran projects with
the Flang runtime.
Providing a definition for that symbol in the Flang runtime might work
correctly for ELF or Mach-O if that symbol has weak linkage in libc++.
But at least for COFF, this now causes multiple-definition errors for
projects that are linking to the Flang runtime and to libc++.

The linker errors before this change for Windows/MinGW using
Clang+Flang+lld look like this:
```
ld.lld: error: duplicate symbol: std::__1::__libcpp_verbose_abort(char const*, ...)
>>> defined at libflang_rt.runtime.a(io-api-minimal.cpp.obj)
>>> defined at libc++.dll.a(libc++.dll)
```

flang-rt/cmake/modules/AddFlangRT.cmake

@@ -238,34 +238,31 @@ function (add_flangrt_library name)
           $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions -fno-rtti -funwind-tables -fno-asynchronous-unwind-tables>
         )
 
-      # We define our own _GLIBCXX_THROW_OR_ABORT here because, as of
-      # GCC 15.1, the libstdc++ header file <bits/c++config> uses
-      # (void)_EXC in its definition of _GLIBCXX_THROW_OR_ABORT to
-      # silence a warning.
-      #
-      # This is a problem for us because some compilers, specifically
-      # clang, do not always optimize away that (void)_EXC even though
-      # it is unreachable since it occurs after a call to
-      # _builtin_abort().  Because _EXC is typically an object derived
-      # from std::exception, (void)_EXC, when not optimized away,
-      # calls std::exception methods defined in the libstdc++ shared
-      # library.  We shouldn't link against that library since our
-      # build version may conflict with the version used by a hybrid
-      # Fortran/C++ application.
-      #
-      # Redefining _GLIBCXX_THROW_OR_ABORT in this manner is not
-      # supported by the maintainers of libstdc++, so future changes
-      # to libstdc++ may require future changes to this build script
-      # and/or future changes to the Fortran runtime source code.
-      target_compile_options(${tgtname} PUBLIC "-D_GLIBCXX_THROW_OR_ABORT(_EXC)=(__builtin_abort())")
+      # Include header at the top of all compilation units to avoid dependency
+      # on the C++ STL (libstdc++ or libc++).
+      target_compile_options(${tgtname} PRIVATE
+          "$<$<COMPILE_LANGUAGE:CXX>:-include${FLANG_RT_SOURCE_DIR}/lib/runtime/stl-overrides.h>"
+        )
     elseif (MSVC)
       target_compile_options(${tgtname} PRIVATE
           $<$<COMPILE_LANGUAGE:CXX>:/EHs-c- /GR->
         )
+
+      # Include header at the top of all compilation units to avoid dependency
+      # on the C++ STL (libstdc++ or libc++).
+      target_compile_options(${tgtname} PRIVATE
+          "$<$<COMPILE_LANGUAGE:CXX>:/FI${FLANG_RT_SOURCE_DIR}/lib/runtime/stl-overrides.h>"
+        )
     elseif (CMAKE_CXX_COMPILER_ID MATCHES "XL")
       target_compile_options(${tgtname} PRIVATE
           $<$<COMPILE_LANGUAGE:CXX>:-qnoeh -qnortti>
         )
+
+      # Include header at the top of all compilation units to avoid dependency
+      # on the C++ STL (libstdc++ or libc++).
+      target_compile_options(${tgtname} PRIVATE
+          "$<$<COMPILE_LANGUAGE:CXX>:-qinclude=${FLANG_RT_SOURCE_DIR}/lib/runtime/stl-overrides.h>"
+        )
     endif ()
 
     # Add target specific options if necessary.

flang-rt/lib/runtime/CMakeLists.txt

@@ -59,6 +59,7 @@ set(supported_sources
   ragged.cpp
   reduction.cpp
   stat.cpp
+  stl-overrides.cpp
   stop.cpp
   sum.cpp
   support.cpp

flang-rt/lib/runtime/io-api-minimal.cpp

@@ -146,19 +146,4 @@ bool IODEF(OutputLogical)(Cookie cookie, bool truth) {
 
 } // namespace Fortran::runtime::io
 
-#if defined(_LIBCPP_VERBOSE_ABORT)
-// Provide own definition for `std::__libcpp_verbose_abort` to avoid dependency
-// on the version provided by libc++.
-
-void std::__libcpp_verbose_abort(char const *format, ...) noexcept(
-    noexcept(std::__libcpp_verbose_abort(""))) {
-  va_list list;
-  va_start(list, format);
-  std::vfprintf(stderr, format, list);
-  va_end(list);
-
-  std::abort();
-}
-#endif
-
 RT_EXT_API_GROUP_END

flang-rt/lib/runtime/stl-overrides.cpp

@@ -0,0 +1,22 @@
+//===-- lib/runtime/stl-overrides.cpp ---------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
+
+// Provide function that is used in place of `std::__libcpp_verbose_abort` to
+// avoid dependency on the symbol provided by libc++.
+void flang_rt_verbose_abort(char const *format, ...) {
+  va_list list;
+  va_start(list, format);
+  std::vfprintf(stderr, format, list);
+  va_end(list);
+
+  std::abort();
+}

flang-rt/lib/runtime/stl-overrides.h

@@ -0,0 +1,38 @@
+//===-- lib/runtime/stl-overrides.h -----------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// This file is inserted implicitly to all translation units using -include on
+// the command line.  The reason is that it configures the C++ standard
+// template library (libc++ or libstdc++) using preprocessor macro definitions
+// that must appear before any C++ library include.
+
+// We define our own _GLIBCXX_THROW_OR_ABORT here because, as of GCC 15.1, the
+// libstdc++ header file <bits/c++config> uses (void)_EXC in its definition of
+// _GLIBCXX_THROW_OR_ABORT to silence a warning.
+//
+// This is a problem for us because some compilers, specifically clang, do not
+// always optimize away that (void)_EXC even though it is unreachable since it
+// occurs after a call to _builtin_abort().  Because _EXC is typically an
+// object derived from std::exception, (void)_EXC, when not optimized away,
+// calls std::exception methods defined in the libstdc++ shared library.  We
+// shouldn't link against that library since our build version may conflict
+// with the version used by a hybrid Fortran/C++ application.
+//
+// Redefining _GLIBCXX_THROW_OR_ABORT in this manner is not supported by the
+// maintainers of libstdc++, so future changes to libstdc++ may require future
+// changes to this build script and/or future changes to the Fortran runtime
+// source code.
+#define _GLIBCXX_THROW_OR_ABORT(_EXC) (__builtin_abort())
+
+// Declare function that is used in place of `std::__libcpp_verbose_abort` to
+// avoid dependency on the symbol provided by libc++.
+#ifndef _LIBCPP_VERBOSE_ABORT
+#define _LIBCPP_VERBOSE_ABORT(...) flang_rt_verbose_abort(__VA_ARGS__)
+void flang_rt_verbose_abort(char const *format, ...)
+    __attribute__((format(printf, 1, 2)));
+#endif