[libcxx-commits] [libcxx] [libc++][NFC] Refactor _LIBCPP_AVAILABILITY_HAS_* macros to always be defined (PR #71002)

[Louis Dionne via libcxx-commits]

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

This LGTM, it makes it harder to misuse these macros.

https://github.com/llvm/llvm-project/pull/71002