[clang] [Clang] Avoid querying tag definitions for invalid DeclSpecs (PR #210085)

[Tony Guillot via cfe-commits]

https://github.com/to268 approved this pull request.

LGTM! But there is a dangling new line remaining in the release notes that should be removed to avoid merge conflicts with the release branch (no changes of this file should appear).

https://github.com/llvm/llvm-project/pull/210085