If ppoll(2) exits, log to syslog(3) instead of stderr

If ppoll(2) exits, log to syslog(3) instead of stderr

By default cron runs as a daemon, with stderr redirected to /dev/null.
Better not exit silently, as spotted by sthen@, danj@, "wxallowed" on
irc/libera and myself.  There probably is a bug lurking in ppoll(2)
usage or in the syscall implementation.

ok millert@