Deadlock in all Qt3D examples

None of the Qt3D examples work. There is a deadlock where the render thread is waiting on `m_submitRenderViewsSemaphore` and the command thread waits for `m_waitForStartSemaphore` (if I recall correctly - on a different machine now, so I need to make a new build to verify).

Steps to reproduce: Clone latest qt5.git and checkout branch 5.11 for qt3d. Build in debug mode.