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/dll_init.h

@@ -86,6 +86,7 @@ public:
     hold = &start;
     return inext ();
   }
+  friend void dll_global_dtors ();
 };
 
 extern dll_list dlls;