[REG: 6.5->6.8] ios: Fails if main app target is in a subdirectory

[cmake] The custom command generating
[cmake]
[cmake] /Users/user/qtbug136736/mainapp/MainApp_en_GB.qm
[cmake]
[cmake] is attached to multiple targets:
[cmake]
[cmake] IosTranslations_lrelease
[cmake] MainApp_MainApp_translations
[cmake]
[cmake] but none of these is a common dependency of the other(s). This is not
[cmake] allowed by the Xcode "new build system".