[libcxx-commits] [libcxx] [libc++] Deprecate the C++20 synchronization library before C++20 (PR #86410)

[Mark de Wever via libcxx-commits]

https://github.com/mordante approved this pull request.

Basically LGTM but I prefer to keep the tests working until we remove support.

https://github.com/llvm/llvm-project/pull/86410