[libcxx-commits] [libcxx] [libc++] Use public os_sync API instead of private __ulock on newer Apple platforms (PR #182947)

[Louis Dionne via libcxx-commits]

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ldionne wrote:

As @huixie90 pointed out just now in the live review, we could also just assume that `__ulock` is provided on all Apple platforms and then just unconditionally fall back to it. That would simplify the code somewhat.

https://github.com/llvm/llvm-project/pull/182947