sim: parse_args: display getopt error ourselves

Fix a long standing todo where we let getopt write directly to stderr
when an invalid option is passed.  Use the sim io funcs instead as they
go through the filtered callbacks that gdb wants.

sim/lm32/sim-if.c

@@ -121,9 +121,7 @@ sim_open (kind, callback, abfd, argv)
       return 0;
     }
 
-  /* getopt will print the error message so we just have to exit if this fails.
-     FIXME: Hmmm...  in the case of gdb we need getopt to call
-     print_filtered.  */
+  /* The parser will print an error message for us, so we silently return.  */
   if (sim_parse_args (sd, argv) != SIM_RC_OK)
     {
       free_state (sd);