[cxx-interop] Generate memberwise initializers for non-C++ types.

Previously, when we checked for `!hasUserDeclaredConstructor` rather than
`isAggregate`, we would always generate memberwise initializers for C
record types. This updates the isAggregate to be true for non-C++ types
so we will generate memberwise initializers for them as well.

Author: zoecarver

lib/ClangImporter/ImportDecl.cpp

@@ -3452,7 +3452,7 @@ namespace {
         ctors.push_back(createDefaultConstructor(Impl, result));
       }
 
-      bool isAggregate = cxxRecordDecl && cxxRecordDecl->isAggregate();
+      bool isAggregate = !cxxRecordDecl || cxxRecordDecl->isAggregate();
       if (hasReferenceableFields && hasMemberwiseInitializer && isAggregate) {
         // The default zero initializer suppresses the implicit value
         // constructor that would normally be formed, so we have to add that