This was an unfortunate copypasta error that slipped in with 9836d6d. 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.
This should ease testing and deployment in simpler cases
If present, it overrides DOCUMENT_ROOT and SCRIPT_NAME and prevents mangling of PATH_INFO. Should allow cleaner configs when script names don't come from request URIs directly.
He's been added to the contributors in README.rst.