[clang] [Clang] Avoid assertion failure for initialized extern aliases (PR #223124)

[Aaron Ballman via cfe-commits]

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@@ -14127,6 +14093,15 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     return;
   }
 
+  // handleAliasAttr() runs before the initializer is attached to the VarDecl,
+  // so it cannot determine that an extern declaration with an initializer is a
+  // definition. Diagnose the conflict now that an initializer is present and
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AaronBallman wrote:

I think for this case it would make sense on redeclaration merging. CC @erichkeane in case he has better ideas because this is starting to spread the checking out an awful lot.

`Sema::FinalizeDeclaration()` is another place to consider, but I suspect it may be similar to adding the logic to `AddInitializerToDecl()`...

https://github.com/llvm/llvm-project/pull/223124