pack: move pack-closing functions

The function close_pack_fd() needs to be temporarily made global. Its
scope will be restored to static in a subsequent commit.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/merge.c b/builtin/merge.c
index 328945d..dfd6830 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -32,6 +32,7 @@
 #include "gpg-interface.h"
 #include "sequencer.h"
 #include "string-list.h"
+#include "packfile.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)