* autoload.cc (PrivilegeCheck): Define.

* fhandler.cc (fhandler_base::open): Always try opening with backup
	resp. restore intent.
	* fhandler_disk_file.cc (fhandler_disk_file::opendir): Always try
	opening with backup intent.
	(fhandler_disk_file::readdir): Ditto when trying to retrieve file id
	explicitely.
	* security.cc (check_file_access): Replace pbuf with correctly
	PPRIVILEGE_SET typed pset.  Check explicitely for backup and/or restore
	privileges when AccessCheck fails, to circumvent AccessCheck
	shortcoming.  Add comment to explain.

winsup/cygwin/fhandler_disk_file.cc

@@ -1606,6 +1606,7 @@ fhandler_disk_file::opendir ()
 				   SYNCHRONIZE | FILE_LIST_DIRECTORY,
 				   &attr, &io, wincap.shared (),
 				   FILE_SYNCHRONOUS_IO_NONALERT
+				   | FILE_OPEN_FOR_BACKUP_INTENT
 				   | FILE_DIRECTORY_FILE);
 	      if (!NT_SUCCESS (status))
 		{
@@ -1869,7 +1870,7 @@ go_ahead:
 	      InitializeObjectAttributes (&attr, &upath, OBJ_CASE_INSENSITIVE,
 					  dir->__handle , NULL);
 	      if (!NtOpenFile (&hdl, READ_CONTROL, &attr, &io,
-			       wincap.shared (), 0))
+			       wincap.shared (), FILE_OPEN_FOR_BACKUP_INTENT))
 		{
 		  de->d_ino = readdir_get_ino_by_handle (hdl);
 		  CloseHandle (hdl);