[clang] Raise an error on namespace aliases with qualified names. (PR #86122)

[Daniel M. Katz via cfe-commits]

katzdm wrote:

> You can ignore the merge conflicts in the release notes; it’s better to let whoever ends up merging this (probably me) take care of that when it comes to the release notes (because they get updated constantly).

Ah, missed this - already fixed it. Will ignore if it happens again.

https://github.com/llvm/llvm-project/pull/86122