Windows: permit clean when switching platforms

Windows: permit clean when switching platforms

When switching between i386 and amd64 in the same build tree
the "clean" make directive would fail due to NTLang.bat not
having been built in the new platform's destination directory.
Force NTLang.bat to be built as a dependency of cleanup and
delete it at the end along with the version files.

Change-Id: I49a44204c636ab9ad89be44d4fad20ed6050fdda
Reviewed-on: http://gerrit.openafs.org/3615
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>