Fix race condition
kcfg/kscreensaversettingsbase.kcfgc is used for two different targets:
- kscreenlocker library
- kscreenlocker_greet
Only one of the two is actually asking to create the moc, so when building in parallel, the moc may need to be included, but would not be created yet, causing build failures.
This was seen on openSUSE's OBS.