cache.h: flip NO_THE_INDEX_COMPATIBILITY_MACROS switch

By default, index compat macros are off from now on, because they
could hide the_index dependency.

Only those in builtin can use it.

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

builtin/pull.c

@@ -5,6 +5,7 @@
  *
  * Fetch one or more remote refs and merge it/them into the current HEAD.
  */
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "cache.h"
 #include "config.h"
 #include "builtin.h"