ll-merge: replace flag argument with options struct

Keeping track of the flag bits is proving more trouble than it's
worth.  Instead, use a pointer to an options struct like most similar
APIs do.

Callers with no special requests can pass NULL to request the default
options.

Cc: Bert Wesarg <bert.wesarg@googlemail.com>
Cc: Avery Pennarun <apenwarr@gmail.com>
Helped-by: Justin Frankel <justin@cockos.com>
Helped-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -155,7 +155,7 @@ static int checkout_merged(int pos, struct checkout *state)
 	 * merge.renormalize set, too
 	 */
 	status = ll_merge(&result_buf, path, &ancestor, "base",
-			  &ours, "ours", &theirs, "theirs", 0);
+			  &ours, "ours", &theirs, "theirs", NULL);
 	free(ancestor.ptr);
 	free(ours.ptr);
 	free(theirs.ptr);