[llvm] Export LLVM plugin entrypoint for windows shared library builds (PR #115431)

[Thomas Fransham via llvm-commits]

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@@ -107,7 +107,7 @@ class PassPlugin {
 ///   };
 /// }
 /// ```
-extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK
+extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK LLVM_ABI_EXPORT
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fsfod wrote:

I could change it to that or maybe make a new macro for plugins with a TODO note, I guess i could also remove LLVM_ATTRIBUTE_WEAK for windows builds as well.

> How does this work within LLVM however? The declaration should be:

I don't think it would ever be used in a dllimport mode since there can be multiple plugins.

https://github.com/llvm/llvm-project/pull/115431