run: fix extra emulator args that were broken by -X

run

@@ -140,16 +140,18 @@ done
 shift "$(($OPTIND - 1))"
 extra_flags="$extra_flags $@"
 OPTIND=1
-while getopts b OPT $extra_opts; do
-  case "$OPT" in
-    b)
-      gem5_fsbiglittle=true
-      ;;
-    ?)
-      exit 2
-      ;;
-  esac
-done
+if [ -n "$extra_opts" ]; then
+  while getopts b OPT $extra_opts; do
+    case "$OPT" in
+      b)
+        gem5_fsbiglittle=true
+        ;;
+      ?)
+        exit 2
+        ;;
+    esac
+  done
+fi
 set_common_vars -L "$common_linux_variant" -M "$common_gem5_variant" -n "$common_run_id" "$arch" "$gem5"
 if "$debug" && "$kvm"; then
   echo 'error: -d and -K are incompatible' 1>&2