[clang] [clang] Update diagnostics for type aware allocators (PR #148576)

[Corentin Jabot via cfe-commits]

================
@@ -10081,11 +10081,8 @@ def err_destroying_operator_delete_not_usual : Error<
 def err_type_aware_destroying_operator_delete : Error<
   "destroying delete is not permitted to be type aware">;
 
-def ext_cxx26_type_aware_allocators : ExtWarn<
-  "type aware allocators are a C++2c extension">, InGroup<CXX26>;
-def warn_cxx26_type_aware_allocators : Warning<
-  "type aware allocators are incompatible with C++ standards before C++2c">,
-  DefaultIgnore, InGroup<CXXPre26Compat>;
+def warn_ext_type_aware_allocators : ExtWarn<
+  "type aware allocators are a clang extension">, InGroup<DiagGroup<"cxx-type-aware-allocators">>;
----------------
cor3ntin wrote:

```suggestion
  "type aware allocators are a Clang extension">, InGroup<DiagGroup<"cxx-type-aware-allocators">>;
```

https://github.com/llvm/llvm-project/pull/148576