[darwin] libproc: fix missing declaration

In previous attempt to handle -fno-common, I fixed the multiple
declaration issue, but I forgot to add the declaration in dstore.c.

Signed-off-by: Jiajie Chen <c@jia.je>

dialects/darwin/libproc/dstore.c

@@ -42,6 +42,7 @@ static char copyright[] =
 
 #include "lsof.h"
 
+struct file *Cfp;			/* curent file's file struct pointer */
 
 #if	defined(HASFSTRUCT)
 /*