login_tty: Make the replacement code work on BSD systems.
* lib/login_tty.c: Include <sys/ioctl.h>.
(login_tty): Use ioctl TIOCSCTTY when available.
* modules/login_tty (Depends-on): Add sys_ioctl.
Reported by Mats Erik Andersson <mats.andersson@gisladisker.se>.