Do not use global variable in function, pass parameter instead.

[goodpaperman]

simple type mistake, only reproduct on macOS (?)
'optarg' is a global variable, can be used directly,
but macOS choked on that ,
and I see all other functions passing a parameter instead the global variable,
so here just add a function parameter.

Signed-off-by: yunh [email protected]

[emcrisostomo]

I can't reproduce it. However, I agree that we should not use the global variable there.