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

[Louis Dionne via libcxx-commits]

https://github.com/ldionne requested changes to this pull request.

I'd like to see if we can improve our test suite before we land this. I'll make a pass at this.

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