Build broken on any platform lacking systemd
a8999acc which was supposed to fix building of the systemd watchdog broke building on any platform without systemd. Just reverting that commit for now seems like the wrong idea, however, because the underlying issue still exists which isn't being addressed at all - the systemd configure check fails. I have a patch in branch systemd209 in my repo, but building that on my systemd-enabled jessie produces linking errors at the very end. I'm not too well versed in the systemd world, our entire detection magic needs to be checked for all cases because right now we even get the non-corner cases wrong.
This was first reported by Toralf Förster email@example.com on #tor-dev as indicated in my commit msg