[clang] [clang][Sema] Accept gnu format attributes (PR #160255)

[via cfe-commits]

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@@ -268,6 +268,9 @@ Attribute Changes in Clang
   attribute, allowing the attribute to only be attached to the declaration. Prior, this would be
   treated as an error where the definition and declaration would have differing types.
 
+- New format attributes ``gnu_printf``, ``gnu_scanf``, ``gnu_strftime`` and ``gnu_strfmon`` are added
+  as aliases for ``printf``, ``scanf``, ``strftime`` and ``strfmon``.
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Sirraide wrote:

```suggestion
  as aliases for ``printf``, ``scanf``, ``strftime`` and ``strfmon``. (#GH16219)
```

https://github.com/llvm/llvm-project/pull/160255