[libcxx-commits] [libcxx] [libc++] Provide flag for RUNTIMES_USE_LIBC=llvm-libc (PR #174967)

[William Huynh via libcxx-commits]

https://github.com/saturn691 approved this pull request.

LGTM, but I think someone from llvm/reviewers-libcxx should also have a look

https://github.com/llvm/llvm-project/pull/174967