Remove all void-pointer arithmetic.

ANSI C99 doesn't allow void-pointer arithmetic. This patch fixes this in
various ways. Usually the strategy that required the least changes was used.

Signed-off-by: Florian Forster <octo@verplant.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diffcore-order.c

@@ -30,7 +30,7 @@ static void prepare_order(const char *orderfile)
 	close(fd);
 	if (map == MAP_FAILED)
 		return;
-	endp = map + st.st_size;
+	endp = (char *) map + st.st_size;
 	for (pass = 0; pass < 2; pass++) {
 		cnt = 0;
 		cp = map;