monitor: rename EVENT_* to QEVENT_* to avoid conflict on mingw32

Partially fixes mingw32 build.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/vl.c b/vl.c
index 96ab020..1981e6e 100644
--- a/vl.c
+++ b/vl.c
@@ -4103,11 +4103,11 @@
         } while (vm_can_run());
 
         if (qemu_debug_requested()) {
-            monitor_protocol_event(EVENT_DEBUG, NULL);
+            monitor_protocol_event(QEVENT_DEBUG, NULL);
             vm_stop(EXCP_DEBUG);
         }
         if (qemu_shutdown_requested()) {
-            monitor_protocol_event(EVENT_SHUTDOWN, NULL);
+            monitor_protocol_event(QEVENT_SHUTDOWN, NULL);
             if (no_shutdown) {
                 vm_stop(0);
                 no_shutdown = 0;
@@ -4115,17 +4115,17 @@
                 break;
         }
         if (qemu_reset_requested()) {
-            monitor_protocol_event(EVENT_RESET, NULL);
+            monitor_protocol_event(QEVENT_RESET, NULL);
             pause_all_vcpus();
             qemu_system_reset();
             resume_all_vcpus();
         }
         if (qemu_powerdown_requested()) {
-            monitor_protocol_event(EVENT_POWERDOWN, NULL);
+            monitor_protocol_event(QEVENT_POWERDOWN, NULL);
             qemu_irq_raise(qemu_system_powerdown);
         }
         if ((r = qemu_vmstop_requested())) {
-            monitor_protocol_event(EVENT_STOP, NULL);
+            monitor_protocol_event(QEVENT_STOP, NULL);
             vm_stop(r);
         }
     }