For these annotations to do anything you need `-Wthread-safety`, in
which case users most likely enable them anyways. This avoids that users
have to explictly define a macro just to use the feature they already
had to opt-in to.
`__has_cpp_attribute(__nodiscard__)` is always true now, so we might as
well replace `_LIBCPP_NODISCARD`. It's one less macro that can result in
bad diagnostics.
This change makes `std::lock_guard` available when
`_LIBCPP_HAS_NO_THREADS` is set. This class is generic and doesn't
require threading support, and is regularly used even in environments
where threading isn't available like embedded.
fixes#89891
---------
Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
This also updates the moved code to the current style. (i.e. `_VSTD` -> `std`, `_LIBCPP_INLINE_VISIBILITY` -> `_LIBCPP_HIDE_FROM_ABI`, clang-format).
Reviewed By: Mordante, #libc, EricWF
Spies: arichardson, libcxx-commits, mikhail.ramalho
Differential Revision: https://reviews.llvm.org/D146228
