Revert "[C++20] [Modules] Trying to compare the trailing require clau…

…se from the primary template function"

This reverts commit 9e50578. Since it
looks like this one prevents us to fix the modular build for libcxx.

clang/lib/AST/ASTContext.cpp

@@ -6683,28 +6683,8 @@ bool ASTContext::isSameEntity(const NamedDecl *X, const NamedDecl *Y) const {
         return false;
     }
 
-    // The trailing require clause of instantiated function may change during
-    // the semantic analysis. Trying to get the primary template function (if
-    // exists) to compare the primary trailing require clause.
-    auto TryToGetPrimaryTemplatedFunction =
-        [](const FunctionDecl *FD) -> const FunctionDecl * {
-      switch (FD->getTemplatedKind()) {
-      case FunctionDecl::TK_DependentNonTemplate:
-        return FD->getInstantiatedFromDecl();
-      case FunctionDecl::TK_FunctionTemplate:
-        return FD->getDescribedFunctionTemplate()->getTemplatedDecl();
-      case FunctionDecl::TK_MemberSpecialization:
-        return FD->getInstantiatedFromMemberFunction();
-      case FunctionDecl::TK_FunctionTemplateSpecialization:
-        return FD->getPrimaryTemplate()->getTemplatedDecl();
-      default:
-        return FD;
-      }
-    };
-    const FunctionDecl *PrimaryX = TryToGetPrimaryTemplatedFunction(FuncX);
-    const FunctionDecl *PrimaryY = TryToGetPrimaryTemplatedFunction(FuncY);
-    if (!isSameConstraintExpr(PrimaryX->getTrailingRequiresClause(),
-                              PrimaryY->getTrailingRequiresClause()))
+    if (!isSameConstraintExpr(FuncX->getTrailingRequiresClause(),
+                              FuncY->getTrailingRequiresClause()))
       return false;
 
     auto GetTypeAsWritten = [](const FunctionDecl *FD) {