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

[Osama Abdelkader via cfe-commits]

osamakader wrote:

> After merging this PR, you need to follow the documentation on [how to backport a commit to the release branch](https://llvm.org/docs/GitHub.html#releases). Do you need this PR to be merged on your behalf?

Yes, please. I don't have permission to merge.

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