Changes suggested by Dave Korn.

* dcrt0.cc (cygwin_exit): Remove (hopefully) extraneous call to
dll_global_dtors.
* dll_init.cc (dll_global_dtors): Run destructors in reverse dependency/load
order.
* dll_init.h (dll_list): Add dll_global_dtors as a friend.

winsup/cygwin/dcrt0.cc

@@ -1112,7 +1112,6 @@ cygwin_atexit (void (*function)(void))
 extern "C" void
 cygwin_exit (int n)
 {
-  dll_global_dtors ();
   if (atexit_lock)
     atexit_lock.acquire ();
   exit (n);