Require out-of-source build
Summary: KService doesn't build if you try to do an in-source build (fakeplugin.desktop gets renamed in the wrong place and CMake dies), so let's just require an out-of-source build, which people should be doing anyway.
- Builds with an out-of-source build
- Stops immediately if you try to do an in-source build
Reviewers: dfaure, cfeck, Frameworks
Reviewed By: dfaure
Differential Revision: https://phabricator.kde.org/D14003