parse-options: allow ll_callback with OPTION_CALLBACK

OPTION_CALLBACK is much simpler/safer to use, but parse_opt_cb does
not allow access to parse_opt_ctx_t, which sometimes is useful
(e.g. to obtain the prefix).

Extending parse_opt_cb to take parse_opt_cb could result in a lot of
changes. Instead let's just allow ll_callback to be used with
OPTION_CALLBACK. The user will have to be careful, not to change
anything in ctx, or return wrong result code. But that's the price for
ll_callback.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options-cb.c

@@ -171,8 +171,10 @@ int parse_opt_noop_cb(const struct option *opt, const char *arg, int unset)
  * parse_options().
  */
 enum parse_opt_result parse_opt_unknown_cb(struct parse_opt_ctx_t *ctx,
-					   const struct option *opt, int unset)
+					   const struct option *opt,
+					   const char *arg, int unset)
 {
+	BUG_ON_OPT_ARG(arg);
 	return PARSE_OPT_UNKNOWN;
 }