[libcxx-commits] [libcxx] Replace uses of `__libcpp_ctz` by `__countr_zero` (PR #132639)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Closing per @winner245 's comment -- we already have a patch ready to go once Clang 18 is dropped, and this patch as-is doesn't implement all that we wanted from https://github.com/llvm/llvm-project/issues/131179.

https://github.com/llvm/llvm-project/pull/132639