Fix build with -fno-common

Index: transcript.c
--- transcript.c.orig
+++ transcript.c
@@ -46,7 +46,7 @@ struct list			*exclude_list;
 char				*path_prefix = NULL;
 int				edit_path;
 int				skip;
-int				cksum;
+extern int			cksum;
 int				fs_minus;
 int				exclude_warnings = 0;
 FILE				*outtran;