[llvm] [LLVM Demangler] Set `InConstraintExpr` to `true` when demangling a c… (PR #107385)

[Haojian Wu via llvm-commits]

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@@ -5737,6 +5737,7 @@ Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParamDecl(
   }
 
   if (consumeIf("Tk")) {
+    ScopedOverride<bool> SaveInConstraintExpr(InConstraintExpr, true);
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hokein wrote:

Since this is a temporary fix, it would be helpful to add comments that explain both what the newly-added line of code is doing and why it’s necessary for now. 

https://github.com/llvm/llvm-project/pull/107385