misc: Bugfix for Freezing Terminal in SystemC Simulation

If the terminal was used in the SystemC or TLM simulations the simulation gets
in a deadlock state. This is because of the Event queue gets locked while
servicing the async events leading to event queue deadlock. This was solved by
locking the queue at the beginning of service of async events.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

util/systemc/sc_module.cc

@@ -140,6 +140,7 @@ void
 Module::serviceAsyncEvent()
 {
     EventQueue *eventq = getEventQueue(0);
+    std::lock_guard<EventQueue> lock(*eventq);
 
     assert(async_event);