[clang] [clang] Fix `gnu::init_priority` attribute handling for reserved values (PR #121577)

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@@ -510,6 +510,7 @@ def PrivateModule : DiagGroup<"private-module">;
 def CXX11InlineNamespace : DiagGroup<"c++11-inline-namespace">;
 def InlineNamespaceReopenedNoninline
     : DiagGroup<"inline-namespace-reopened-noninline">;
+def InitPriorityReserved : DiagGroup<"init-priority-reserved">;
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el-ev wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/121577