[clang] More fixes for P3144R2 implementation (PR #149406)

[Erich Keane via cfe-commits]

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

Marking as 'requested changes' so this doesn't get inadvertently merged while discussions re: the diagnostics are happening.

https://github.com/llvm/llvm-project/pull/149406