symlinks.h: move declarations for symlinks.c functions from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff-lib.c b/diff-lib.c
index d292405..60e979d 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -14,6 +14,7 @@
 #include "unpack-trees.h"
 #include "refs.h"
 #include "submodule.h"
+#include "symlinks.h"
 #include "trace.h"
 #include "dir.h"
 #include "fsmonitor.h"