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

[William Tran-Viet via libcxx-commits]

================

----------------
smallp-o-p wrote:

`_Val` should've been a regular function parameter in the first place, I plan on addressing all of these + another nit I spotted on a change I made.

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