Patch to get arm running on FreeBSD again

8dbea0fa broke arm on FreeBSD for me.

$ ./arm get_bsd_jail_id() takes exactly 1 argument (0 given)

The attached patch gets arm running again.

The jail detection appears to still be broken, but this seems to be an unrelated problem and I rediscovered some patches in a stem branch that look relevant.

I'll file a stem ticket about this once I have more information.