Correct invalid defintion in configuring systemd support
Correct invalid defintion in configuring systemd support

This was an unfortunate copypasta error that slipped in with 9836d6d22.
The HAVE_SYSTEMD macro should only be defined based on the presence of
the library, not the unit files, since the units are useless without the
library support.

muthhus/fcgiwrap,gnosek/fcgiwrap,samboy/fcgiwrap,samboy/fcgiwrap