Fix frameworks compilation with Qt < 5.6
Review Request #129065 - Created Sept. 28, 2016 and submitted
QQuickWindow::NoStage was new in Qt5.6. This uses a value that's valid in earlier Qt. This shouldn't have any behavioural effect.
Ran on my nvidia machine and moused over the taskbar.
I got thumbnails as expected, but also Nvidia-settings shows "user dedicated memory" remaining constant