[clang] [Clang] disallow selectany on non-global-variable declarations (PR #189641)

[Aaron Ballman via cfe-commits]

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@@ -4477,6 +4477,7 @@ def DLLImportStaticLocal : InheritableAttr, TargetSpecificAttr<TargetHasDLLImpor
 
 def SelectAny : InheritableAttr {
   let Spellings = [Declspec<"selectany">, GCC<"selectany">];
+  let Subjects = SubjectList<[GlobalVar], ErrorDiag>;
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AaronBallman wrote:

I would expect changes in SemaDeclAttr.cpp to remove the use of `err_attribute_selectany_non_extern_data` from `checkSelectAnyAttr()`, but I am curious why `isExternallyVisible()` was insufficient there. Regardless, I think this needs a different subject because local static variables cannot be `selectany`: https://github.com/llvm/llvm-project/blob/6446435534746effdb2bedf6127bdf996f9fd3f0/clang/include/clang/AST/Decl.h#L1237

https://github.com/llvm/llvm-project/pull/189641