[clang] [clang][NFC] Mark CWG2629 as implemented and add a test (PR #195490)

[Vlad Serebrennikov via cfe-commits]

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

> Would you prefer that I did multiple DRs per PR (assuming none of them require compiler changes)? I've been doing 1 per PR so far, and I worry I'm being annoying by opening a bunch of tiny PRs.

Tiny PRs are very nice to review (and revert if needed), so keep it up!

> Clang however has always rejected both: https://godbolt.org/z/GYc4hhrnz

In my experience, Clang versions prior to 3.3 are prone to regressions quite a bit, especially in C++0x mode, so when you're checking since when we're handling examples correctly, it makes sense to check all version between 2.7 and 3.3. CWG2629 in particular is clear in this regard, so this is good to go.

https://github.com/llvm/llvm-project/pull/195490