[libcxx-commits] [libcxx] [libc++][NFC] Simplify `gcd` a bit (PR #173570)

[Thibault Monnier via libcxx-commits]

https://github.com/Thibault-Monnier approved this pull request.

LGTM except for one comment.

https://github.com/llvm/llvm-project/pull/173570