[libcxx-commits] [libcxx] [libc++] Improves _LIBCPP_HAS_NO_THREADS guards. (PR #76624)

[Louis Dionne via libcxx-commits]

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

This LGTM. However, at some point I think we'll need to revisit how we handle `_LIBCPP_HAS_NO_THREADS` and `_LIBCPP_HAS_NO_LOCALIZATION`. I think we'll want to make the contents of headers empty in the case where they're not supported, like we do for e.g. `_LIBCPP_HAS_NO_RANDOM_DEVICE`. This will merit more discussion anyway, and doesn't impact whether this patch should land.

https://github.com/llvm/llvm-project/pull/76624