XQuartz: pbproxy standalone: added missing variable declarations.

(cherry picked from commit 2d947d17a3ef5fb8cef959bff0eb08b8bb5b6548)

hw/xquartz/pbproxy/app-main.m

@@ -50,6 +50,9 @@ static void signal_handler (int sig) {
 }
 
 int main (int argc, const char *argv[]) {
+    const char *s;
+    int i;
+
 #ifdef DEBUG
     printf("pid: %u\n", getpid());
 #endif