[libcxx-commits] [libcxx] [libc++] Optimize standard streams with sync_with_stdio(false) (PR #209161)

[Louis Dionne via libcxx-commits]

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

I added some more test coverage (first draft with Claude, then reviewed and modified).

LGTM now, but please have a look and let me know if you're OK with the added test coverage.

https://github.com/llvm/llvm-project/pull/209161