open_posix_testsuite/.../pthread_once: Fix.

* Remove the return from a function returning void

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
open_posix_testsuite/.../sched_setscheduler: Fix.

* Change exit() to plain return

* Silence unused warnings

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>