* win32-nat.c (struct so_stuff): Add objfile *objfile field needed to be able

* win32-nat.c (struct so_stuff): Add objfile *objfile field needed to be able
to remove the DLL when unloaded.  Remove unused last field.
(handle_unload_dll): New function to handle unloading of DLL.
(solib_symbols_add): Change return type to struct objfile *.
(get_child_debug_event): Call handle_unload_dll function.