vl.c: Tidy up message printed when we exit on a signal

Tidy up the message printed when qemu exits due to a signal, so that
it's clearer where the message is coming from and that it's not just
stray debug output.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Acked-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

vl.c

@@ -1169,8 +1169,15 @@ int qemu_shutdown_requested(void)
 void qemu_kill_report(void)
 {
     if (shutdown_signal != -1) {
-        fprintf(stderr, "Got signal %d from pid %d\n",
-                         shutdown_signal, shutdown_pid);
+        fprintf(stderr, "qemu: terminating on signal %d", shutdown_signal);
+        if (shutdown_pid == 0) {
+            /* This happens for eg ^C at the terminal, so it's worth
+             * avoiding printing an odd message in that case.
+             */
+            fputc('\n', stderr);
+        } else {
+            fprintf(stderr, " from pid %d\n", shutdown_pid);
+        }
         shutdown_signal = -1;
     }
 }