[libcxx-commits] [libcxx] [libc++] Add CMake plumbing for _LIBCPP_HAS_THREAD_API_C11 mode. (PR #188414)

[Petr Hosek via libcxx-commits]

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

We should consider introducing `LIBCXX_THREAD_API` option with `pthread`, `c11`, `win32` and `external` as possible values, but that's a larger (and potentially breaking) change.

https://github.com/llvm/llvm-project/pull/188414