[libcxx-commits] [libcxx] [libc++] Resolve LWG4308, correct `iterator` availability for `optional<T&>` (PR #173948)

[A. Jiang via libcxx-commits]

https://github.com/frederick-vs-ja approved this pull request.

LGTM. I have some comments on mostly existing issues in the test file. Feel free to delay to a future PR.

https://github.com/llvm/llvm-project/pull/173948