[libcxx-commits] [libcxx] [libc++] Reimplement `optional<T&>` as a partial specialization (PR #201983)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 approved this pull request.

LGTM, but please remove unnecessary metaprogramming in follow-ups.

https://github.com/llvm/llvm-project/pull/201983