Simulator: fix argument parsing.

When getopt_long sets *flag to val, it returns 0.  Previously this
was considered an error. See getopt(3).

simulator/simulator.c

@@ -96,6 +96,9 @@ void sim_start(int argc, char** argv) {
 
   while ((c = getopt_long (argc, argv, shortopts, opts, &index)) != -1)
     switch (c) {
+    case 0:
+      // Long option without short counterpart.
+      break;
     case 'q':
       verbose = 0;
       break;