Honor BUILD_TESTING
Summary: Don't build tests if BUILD_TESTING is OFF.
Test Plan:
- Passed BUILD_TESTING=OFF to cmake, no tests have been built;
- Didn't pass BUILD_TESTING to cmake, all tests have been built.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D13500