numerous "3rdparty" libraries have respective #ifdefs, and consequently
the define is added in several places. it's quite a mess with the .pr?
and .qbs files, though. solve the problem by sidestepping it.

Change-Id: I5a6b1ba7cfe96b44f0a4f4ef9738900906a44316
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>