[clang] [CIR] Make ClangIR compatible with latest nested name specifier AST representation (PR #152846)

[Matheus Izvekov via cfe-commits]

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@@ -138,7 +139,7 @@ isSafeToConvert(const RecordDecl *rd, CIRGenTypes &cgt,
   if (!alreadyChecked.insert(rd).second)
     return true;
 
-  const Type *key = cgt.getASTContext().getTagDeclType(rd).getTypePtr();
+  const Type *key = cgt.getASTContext().getCanonicalTagType(rd).getTypePtr();
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mizvekov wrote:

FYI slightly unrelated, but it might make sense to `assert(rd->isCompleteDefinition()` since some of the uses here only make sense when applied on the definition, such as the `fields` iteration down below.

https://github.com/llvm/llvm-project/pull/152846