monitor: Check whether TCG is enabled before running the "info jit" code

The "info jit" command currently aborts on Mac OS X with the message
"qemu_mutex_lock: Invalid argument" when running with "-M accel=qtest".
We should only call into the TCG code here if TCG has really been
enabled and initialized.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1493179907-22516-1-git-send-email-thuth@redhat.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

monitor.c

@@ -1086,6 +1086,11 @@ static void hmp_info_registers(Monitor *mon, const QDict *qdict)
 
 static void hmp_info_jit(Monitor *mon, const QDict *qdict)
 {
+    if (!tcg_enabled()) {
+        error_report("JIT information is only available with accel=tcg");
+        return;
+    }
+
     dump_exec_info((FILE *)mon, monitor_fprintf);
     dump_drift_info((FILE *)mon, monitor_fprintf);
 }