[llvm] [CFI][annotation] Leave alone function pointers in function annotations (PR #80173)

[via llvm-commits]

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@@ -470,6 +470,9 @@ class LowerTypeTestsModule {
 
   Function *WeakInitializerFn = nullptr;
 
+  GlobalVariable *GlobalAnnotation;
+  std::set<void *> FunctionAnnotations;
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yozhu wrote:

There are quite some uses of `std::set` in this source file, and only one`DenseSet`, so I just selected `std::set`. I can change to use `DenseSet`.

With `void *` I can simply not to worry about casting between types, especially when to query the set to see if it is function annotation. 

https://github.com/llvm/llvm-project/pull/80173