5218 posix definition of NULL
correct unistd.h and iso/stddef_iso.h
update gate source affected

@@ -244,11 +244,11 @@
         get_token(line, &pos, line_len, uid, MISC_SIZE);
         get_token(line, &pos, line_len, gid, MISC_SIZE);
 
         /* Reset these fields... */
 
-        *contents = NULL;
+        *contents = '\0';
         *devnode = '\0';
         *dest = '\0';
 
         /* Handle filetypes which have a last field..... */
         if (type[0] == 'F')