[clang] [clang] Reapply Handle templated operators with reversed arguments (PR #72213)

[Ilya Biryukov via cfe-commits]

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@@ -10088,9 +10088,13 @@ static bool allowAmbiguity(ASTContext &Context, const FunctionDecl *F1,
                            const FunctionDecl *F2) {
   if (declaresSameEntity(F1, F2))
     return true;
-  if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation() &&
-      declaresSameEntity(F1->getPrimaryTemplate(), F2->getPrimaryTemplate())) {
-    return true;
+  if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation()) {
+    auto PT1 = F1->getPrimaryTemplate();
+    auto PT2 = F2->getPrimaryTemplate();
+    if (declaresSameEntity(PT1, PT2) ||
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ilya-biryukov wrote:

Also, I believe the crashes [here](https://buildkite.com/llvm-project/clang-ci/builds/6710#018bcc9e-fdcb-44f8-802e-f5e98303916c) are related: `getCommonPtr()` that you see in the stack trace is called  by `getInstantiatedFromMemberTemplate()`.

https://github.com/llvm/llvm-project/pull/72213