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

[Alexey Samsonov via libcxx-commits]

vonosmas wrote:

> Please wait for a review from @llvm/reviewers-libcxx before landing libc++ patches. I'm not convinced this is the way to go - CC @ldionne

Apologies for misunderstanding, I merged based on Discourse chat and review by Petr, who added original C11-backed implementation. LMK if I should revert this PR, and how/when I can discuss the path forward with maintainers.

There are some related issues we've bumped into when trying to build libc++ threading logic against llvm-libc - e.g. it seems that `__libcpp_thread_id` was an attempt to support opaque implementation-specific thread ID representations, but in practice today it hardcodes the assumption that this must be an integral type.

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