[clang] [clang] Emit diagnostic for typedef+auto missed case in C++98/pre-C23 C (PR #210141)

[Aaron Ballman via cfe-commits]

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

We should also add a release note to `clang/docs/ReleaseNotes.md` but that can be done later because this might eventually be something we want to cherry-pick to the 23.x branch.

https://github.com/llvm/llvm-project/pull/210141