execve.2, fallocate.2, futex.2, sched_rr_get_interval.2, select_tut.2, shmget.2,...

execve.2, fallocate.2, futex.2, sched_rr_get_interval.2, select_tut.2, shmget.2, timer_getoverrun.2, times.2, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_cleanup_push_defer_np.3, pthread_getattr_np.3, pthread_self.3, pthread_setaffinity_np.3, pthread_tryjoin_np.3, sem_open.3, stdin.3, rtc.4, tty_ioctl.4, unix.7: Global fix: s/non-portable/nonportable/

The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>