[clang] [Serialization] Handle uninitialized type constraints (PR #110496)

[Florian Albrechtskirchinger via cfe-commits]

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@@ -1899,7 +1899,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   Record.push_back(D->wasDeclaredWithTypename());
 
   const TypeConstraint *TC = D->getTypeConstraint();
-  assert((bool)TC == D->hasTypeConstraint());
+  Record.push_back(/*TypeConstraintInitialized=*/TC != nullptr);
   if (TC) {
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falbrechtskirchinger wrote:

Because `D->hasTypeConstraint()` does not imply that `D->getTypeConstraint()` is non-null, as the code assumed (hence, the assertion).

https://github.com/llvm/llvm-project/pull/110496