I originally had this return STATUS_USER_APC, but that isn't correct. The
server code here is a bit confusing, but only the thread that waits *during*
the suspend should receive STATUS_USER_APC (and I imagine that it really
should receive STATUS_KERNEL_APC instead). The thread that is suspended
should just keep on waiting.

Besides, we could be suspended for reasons other than to deliver a system
APC.