[tlbuild] Successful build of TL with gcc4 on Cygwin

[Karl Berry]

    The only thing I observe is that now there are a lot (a lot, a lot...)
    of warnings like:

    ../../../../libs/xpdf/xpdf/BuiltinFontTables.cc:330: warning: deprecated
    conversion from string constant to 'char*'

Yes, we see the same.  It is a huge pain.  No one has fixed it.  The
xpdf maintainer is (reportedly) uninterested.  Sigh, sigh, sigh.

karl