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

[A. Jiang via libcxx-commits]

frederick-vs-ja wrote:

> Couldn't replicate the `libc++abi` test failure on my machine running the CI container...

That failure is unrelated to this PR. I think it's OK to merge this PR once CI passes for other builds.

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