Make sure we don't run into warnings for CMake 3.10
Task-number: QTBUG-63442
Change-Id: Ida004705646f0c32fb4bf6006036d80b1f279fd7
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Sebastian Holtermann <sebholt@xwmw.org>
Reviewed-by: Rolf Eike Beer <eb@emlix.com>