If the above requirement is not fullfilled, the following happens:
- pkgconfig/avahi-client.pc is not generated
- $as_echo "#define HAVE_AVAHI /**/" >>confdefs.h will not happen
- cups-browsed says: "Remote support for DNSSD not supported"
This is a silent requirement. Rebuilding avahi with mdnsresponder works as well, but that is because the ebuild will silently enable dbus under that circumstance.