/* Non-typesafe register function. */
void _opt_register(const char *names, enum opt_type type,
char *(*cb)(void *arg),
char *(*cb_arg)(const char *optarg, void *arg),
void (*show)(char buf[OPT_SHOW_LEN], const void *arg),
/* Non-typesafe register function. */
void _opt_register(const char *names, enum opt_type type,
char *(*cb)(void *arg),
char *(*cb_arg)(const char *optarg, void *arg),
void (*show)(char buf[OPT_SHOW_LEN], const void *arg),