[clang] [clang] Fix bogus "deduced type depends on itself" for variable template specializations (PR #217709)

[Younan Zhang via cfe-commits]

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@@ -20715,8 +20715,7 @@ static void DoMarkVarDeclReferenced(
 
   bool NeedDefinition =
       OdrUse == OdrUseContext::Used || NeededForConstantEvaluation ||
-      (TSK != clang::TSK_Undeclared && !UsableInConstantExpr &&
-       Var->getType()->isUndeducedType());
+      (TSK != clang::TSK_Undeclared && Var->getType()->isUndeducedType());
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zyn0217 wrote:

I don't think it makes much sense to allow instantiation within unevaluated context. I question if this should be IFNDR @cor3ntin 

https://github.com/llvm/llvm-project/pull/217709