Add a supposedly deterministic dual-core VideoCommon option, bSyncGPUAtIdleOnly. Basically, the GPU thread continues to start working as soon as the fifo is populated, but instead of indicating completion (via ScheduleEvent_Threadsafe and atomic variables) and causing an interrupt as soon as it's actually done, it sets a flag which the CPU thread handles at certain points - generally on idle (so idle skipping is required). This involves separating CommandProcessor::fifo into a CPU and GPU version (only when the option is on), and copying the former to the latter on SyncGPU(). In theory, this should only desync if the CPU inspects an EFB copy or whatever before getting the interrupt, which should not happen. There are probably bugs in this implementation though. In Melee this does not seem to hurt performance compared to normal dual core. Todo: - see if it actually works - expose this option (currently stuck on) - do something if dual core or idle skipping are off - turn FORCE_WHINE_ABOUT_THREADSAFE off