[libcxx-commits] [libcxx] [libc++] Simplify how the global stream tests are written (PR #66842)

[Louis Dionne via libcxx-commits]

ldionne wrote:

I temporarily added some `UNSUPPORTED` annotations on AIX. It's a bit complicated, but this is needed to unblock a long chain of things:
- Update macOS builders to 13.5
- Update Xcode to 15
- Drop support for older Clangs

https://github.com/llvm/llvm-project/pull/66842