[clang] Reapply "[clang] Fix name lookup for dependent bases" (PR #118003)

[Erich Keane via cfe-commits]

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

Please give @cor3ntin 48 hrs from now to have a chance to review this before committing.

https://github.com/llvm/llvm-project/pull/118003