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>
diff --git a/builtin/reset.c b/builtin/reset.c
index 59898c9..4d18a46 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -7,6 +7,7 @@
  *
  * Copyright (c) 2005, 2006 Linus Torvalds and Junio C Hamano
  */
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "builtin.h"
 #include "config.h"
 #include "lockfile.h"