[tlbuild] Bug in libpng affecting Solaris 10

[Karl Berry]

    I did that, but I didn't manage to get anything useful out of it at

The debugging preprocessor output might go to the file given to -o.

    If you don't want to apply this to the sources, can you please at
    least send me an attempt of a TeX Live-specific patch that does this?

I'll send you something as soon as I can.  I need a little time to think
about it.  -k