[libcxx] [llvm] [libc++] Update macOS and AppleClang (PR #193711)

[Louis Dionne via llvm-commits]

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

LGTM, looks like we're mostly removing a lot of workarounds for older mac systems.

The Windows CI seems unhappy though.

https://github.com/llvm/llvm-project/pull/193711