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/unpack-trees.c b/unpack-trees.c
index c6de2ca..e8a5295 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -18,6 +18,7 @@
 #include "sparse-index.h"
 #include "submodule.h"
 #include "submodule-config.h"
+#include "symlinks.h"
 #include "trace2.h"
 #include "fsmonitor.h"
 #include "object-store.h"