Synchronize VCPU states before reset

This is required to support keeping VCPU states across a system reset.
If we do not read the current state before the reset,
cpu_synchronize_all_post_reset may write back incorrect state
information.

The first user of this will be MCE MSR synchronization which currently
works around the missing cpu_synchronize_all_states.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

vl.c

@@ -1450,6 +1450,7 @@ static void main_loop(void)
         }
         if (qemu_reset_requested()) {
             pause_all_vcpus();
+            cpu_synchronize_all_states();
             qemu_system_reset();
             resume_all_vcpus();
         }