pass the command-line option, which can be specified multiple times,
to another command.
+`OPT_CMDMODE(short, long, &int_var, description, enum_val)`::
+ Define an "operation mode" option, only one of which in the same
+ group of "operating mode" options that share the same `int_var`
+ can be given by the user. `enum_val` is set to `int_var` when the
+ option is used, but an error is reported if other "operating mode"
+ option has already set its value to the same `int_var`.
+
The last element of the array must be `OPT_END()`.