[clang] [clang] Avoid invalidating specialization lookup (PR #196533)

[via cfe-commits]

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@@ -8745,9 +8732,13 @@ bool ASTReader::LoadExternalSpecializationsImpl(
   Deserializing LookupResults(this);
   auto HashValue = StableHashForTemplateArguments(TemplateArgs);
 
-  // Get Decl may violate the iterator from SpecLookups
+  auto It = SpecLookups.find(D);
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mzukovec wrote:

Sure thing. Would that be acceptable? I'm not that familiar with the guidelines here. I can patch those two failing tests if that sounds good for you and you approve this approach.

https://github.com/llvm/llvm-project/pull/196533