commit: use FLEX_ARRAY in struct merge_remote_desc

Convert the name member of struct merge_remote_desc to a FLEX_ARRAY and
use FLEX_ALLOC_STR to build the struct.  This halves the number of
memory allocations, saves the storage for a pointer and avoids an
indirection when reading the name.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.c

@@ -1580,9 +1580,8 @@ void set_merge_remote_desc(struct commit *commit,
 			   const char *name, struct object *obj)
 {
 	struct merge_remote_desc *desc;
-	desc = xmalloc(sizeof(*desc));
+	FLEX_ALLOC_STR(desc, name, name);
 	desc->obj = obj;
-	desc->name = xstrdup(name);
 	commit->util = desc;
 }