(update_archive): Write global extended header if constructed.

src/update.c

@@ -110,7 +110,8 @@ update_archive (void)
 
   name_gather ();
   open_archive (ACCESS_UPDATE);
-
+  xheader_write_global ();
+  
   while (!found_end)
     {
       enum read_header status = read_header (false);