ctfdiff_usage
ctfdiff_usage("Option -%c requires an operand\n",
ctfdiff_usage("Unknown option: -%c\n", optopt);
ctfdiff_usage(NULL);
ctfdiff_usage("-T cannot be used if not diffing types\n");
ctfdiff_usage("-F cannot be used if not diffing functions\n");
ctfdiff_usage("-O cannot be used if not diffing objects\n");