K 10
svn:author
V 3
dim
K 8
svn:date
V 27
2021-12-22T10:13:50.288770Z
K 7
svn:log
V 845
[libcxx] Guard C++20 atomic type aliases

Apply abandoned llvm review https://reviews.llvm.org/D75183 anyway:

The std::atomic_signed_lock_free and std::atomic_unsigned_lock_free
typedefs are a C++20 feature and should be guarded with an #if, so that
they don't get defined in C++17 and prior versions.

Also with the current implementation inclusion of the <atomic> header
will fail the compilation for targets that don't have lock-free atomic
integers (e.g. Armv6-M) because __libcpp_signed_lock_free and
__libcpp_unsigned_lock_free will not get defined. We should not try to
define std::atomic_signed_lock_free and std::atomic_unsigned_lock_free
in this case as well (according to [atomics.alias]/2 these typedefs are
optional in freestanding implementations).

Git Hash:   0e426a4a346876e61adc0b3981a91fe1e039c1ee
Git Author: dim@FreeBSD.org
END