[clang] [Clang] emit -Wignored-qualifiers diagnostic for cv-qualified base classes (PR #121419)

[Erich Keane via cfe-commits]

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

I have a bit of a concern that the template cases are going to be REALLY noisy, but we can deal with restricting individual use cases to a separate warning-group in the future if need-be.

https://github.com/llvm/llvm-project/pull/121419