Use qemu_irq for system_powerdown

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/vl.c b/vl.c
index fdd4f03..a526cb0 100644
--- a/vl.c
+++ b/vl.c
@@ -4281,6 +4281,8 @@
     return 1;
 }
 
+qemu_irq qemu_system_powerdown;
+
 static void main_loop(void)
 {
     int r;
@@ -4321,8 +4323,9 @@
             qemu_system_reset();
             resume_all_vcpus();
         }
-        if (qemu_powerdown_requested())
-            qemu_system_powerdown();
+        if (qemu_powerdown_requested()) {
+            qemu_irq_raise(qemu_system_powerdown);
+        }
         if ((r = qemu_vmstop_requested()))
             vm_stop(r);
     }