Fix build with Qt < 5.10
Fix build with Qt < 5.10

Breakage introduced by a6120f687e.

Change-Id: Id0d0107b303832b364a2ee47b927cd037e5e0959
Reviewed-by: Alexandru Croitor <8ffcaf561685ad82d027def0dc95a2702daba6ec@qt.io>

qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs