make phony_target hack work on mac even with qt 5.1

See also change a4e593c910 in qt-creator.

Change-Id: Ib41c68b9eaa7f844b624179efd24ca5ff31d3ebe
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>