[Frontend] Fix build break after 67c82d6

Remove the `default` label from a switch that covers all cases.

Author: Krzysztof Parzyszek

llvm/utils/TableGen/DirectiveEmitter.cpp

@@ -655,9 +655,8 @@ static void GenerateGetDirectiveAssociation(const DirectiveLanguage &DirLang,
          << "::" << getAssocName(F->second) << ";\n";
     }
   }
-  OS << "  default:\n";
-  OS << "    llvm_unreachable(\"Unexpected directive\");\n";
   OS << "  } // switch(Dir)\n";
+  OS << "  llvm_unreachable(\"Unexpected directive\");\n";
   OS << "}\n";
 }