Use exit_group() instead of exit() on the SIGSYS handler
Use exit_group() instead of exit() on the SIGSYS handler

This change makes is such that if there is a SIGSYS delivered to the
process (and it is handled), it will exit the whole process instead of
just the thread on which the signal was delivered.

omegaup/minijail,omegaup/minijail,omegaup/minijail,omegaup/minijail