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

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 requested changes to this pull request.

> > CC @frederick-vs-ja Thoughts on backporting this if it's good to merge?
> 
> @ldionne WDYT? There're currently some bugs in `optional<T&>` and it might be preferable to backport this PR for easing future fix backport.

We're very close to the next release, so I don't think it's worth back-porting significant amounts of refactoring. 

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