[clang] [Clang] add emit -Wignored-base-class-qualifiers diagnostic for cv-qualified base classes (PR #132116)

[Aaron Ballman via cfe-commits]

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@@ -298,6 +298,8 @@ Improvements to Clang's diagnostics
 
 - Improve the ``-Wundefined-func-template`` warning when a function template is not instantiated due to being unreachable in modules.
 
+- Clang now emits a ``-Wignored-base-class-qualifiers`` diagnostic when a base class includes cv-qualifiers.
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AaronBallman wrote:

```suggestion
- Split diagnosing base class qualifiers from the ``-Wignored-Qualifiers`` diagnostic group into a new ``-Wignored-base-class-qualifiers`` diagnostic group (which is grouped under ``-Wignored-qualifiers``). Fixes #GH131935.
```
(Re-wrapped for 80 column limits.)

https://github.com/llvm/llvm-project/pull/132116