[tlbuild] xindy for x86_64-cygwin

[Karl Berry]

Hi Ken,

    But when the TL2016 pretest starts, am I right that the only change
    needed is the following?

It looks right to me.

    [Or can the two cygwin platforms be lumped together as *-cygwin?  

The * can only be applied at the basename (final) component,
to the best of my knowledge.

    I don't know the syntax of binpattern.]

It seems we never explicitly wrote that binpattern arch names have to be
literal, but as far as I know they do.  FWIW, in TLPSRC.pm there is this
hint for "f" patterns in general:

[...]
=item C<f> I<path>

includes all files which match C<path> where B<only> the last component
of C<path> can contain the usual glob characters C<*> and C<?> (but no
others!).

(At one point I was building all the *.pm documentation for the web/dist
but it seemed no one ever looked at it (including me), so I stopped ... -k)