iothread: fix vcpu stop with smp tcg

Round robin vcpus in tcg_cpu_next even if the vm stopped. This
allows all cpus to enter stopped state.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

vl.c

@@ -3876,14 +3876,15 @@ static void tcg_cpu_exec(void)
     for (; next_cpu != NULL; next_cpu = next_cpu->next_cpu) {
         CPUState *env = cur_cpu = next_cpu;
 
-        if (!vm_running)
-            break;
         if (timer_alarm_pending) {
             timer_alarm_pending = 0;
             break;
         }
         if (cpu_can_run(env))
             ret = qemu_cpu_exec(env);
+        else if (env->stop)
+            break;
+
         if (ret == EXCP_DEBUG) {
             gdb_set_stop_cpu(env);
             debug_requested = 1;