[clang] [llvm] Update llvm::Registry to work for LLVM shared library builds on windows (PR #109024)

[Saleem Abdulrasool via cfe-commits]

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@@ -165,4 +166,8 @@ const std::list<std::unique_ptr<ParsedAttrInfo>> &getAttributePluginInstances();
 
 } // namespace clang
 
+namespace llvm {
+extern template class CLANG_TEMPLATE_ABI llvm::Registry<clang::ParsedAttrInfo>;
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compnerd wrote:

```suggestion
extern template class CLANG_TEMPLATE_ABI Registry<clang::ParsedAttrInfo>;
```

This is already in the `llvm` namespace.

https://github.com/llvm/llvm-project/pull/109024