PowerPC: Set host CPU rounding mode on init and savestate

Not doing this can cause desyncs when TASing. (I don't know
how common such desyncs would be, though. For games that
don't change rounding modes, they shouldn't be a problem.)

Source/Core/Core/HW/CPU.cpp

@@ -87,6 +87,10 @@ static void ExecutePendingJobs(std::unique_lock<std::mutex>& state_lock)
 
 void Run()
 {
+  // Updating the host CPU's rounding mode must be done on the CPU thread.
+  // We can't rely on PowerPC::Init doing it, since it's called from EmuThread.
+  PowerPC::RoundingModeUpdated();
+
   std::unique_lock state_lock(s_state_change_lock);
   while (s_state != State::PowerDown)
   {