We don't want to clip in the desktop process, but we still need it to call
ungrab_clipping_window() if the process that was previously clipping didn't.
This can happen for example when fullscreen clipping is enabled, but the
corresponding window isn't explicitly destroyed before process exit.

The Mac driver doesn't normally steal focus, but a click on the systray icon
counts as the user giving permission.

kernel32: Add a test to show that CreateThread is supposed to fail after the NtTerminateProcess call.