[cairo] cross-compiling on Linux for Windows

[Tor Lillqvist]

> I wish you can build Win32 DLL of zlib.

Of course, it's a bit sad that people have to try so hard to build
zlib themselves, when zlib is one of the few open source libraries
that have an official DLL right on its upstream website... which is
up-to-date and works fine, zlib hasn't changed in years. Why can't
libraries like zlib be considered part of the existing infrastructure,
just like it is on Linux? (Yeah, I know, it's not provided as part of
the operating system, or from the OS vendor through something that
would correspond to Linux package management.)

--tml