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

[Aaron Ballman via cfe-commits]

================
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -std=c++11 -Wignored-qualifiers -verify
+// RUN: %clang_cc1 %s -std=c++11 -Wignored-base-class-qualifiers -verify
----------------
AaronBallman wrote:

Might as well improve test coverage a bit.
```
// RUN: %clang_cc1 %s -std=c++11 -Wignored-base-class-qualifiers -verify
// RUN: %clang_cc1 %s -std=c++11 -Wno-ignored-qualifiers -verify=good
// good-no-diagnostics
```
The second line should disable the warnings hence giving it a new prefix and `no-diagnostics` markings.

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