For those who are providing their own launch images for their iOS
projects then QMAKE_IOS_LAUNCH_SCREEN can be set to point to the
location where the launch image to be used over the default.
[ChangeLog][Platform Specific Changes][iOS] Added support for
specifying a launch image to be used for an iOS project. This can be
achieved by using QMAKE_IOS_LAUNCH_SCREEN.
Change-Id: Ibb236655b282132ab5eee747986a93abb9802200
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>