[cairo] cross-compiling on Linux for Windows

[Tor Lillqvist]

This is getting quite confusing now and I am sorry I entered this
discussion. Let me just restate the facts:

- the name for the zlib DLL that its official site distributes is
zlib1.dll. (Their build is then redistributed by me from the
ftp.gnome.org/download.gnome.org site.)

- an import library for the zlib DLL should be called either libz.a or
libz.dll.a if you want it to be found by mingw ld using the option -lz
. (I am leaving out some other combinations; read the ld documentation
for completeness.)

- there doesn't have to be any direct relation between the name of an
import library and the name of the DLL that the import stubs in the
import library refer to. (Although in most cases, including those
where libtool takes care of naming the DLL and import library, there
of course is a consistent pattern.) (Mingw ld also knows to
automatically generate import stubs on the fly if you mention a DLL on
the command line, but I generally don't take advantage of that
feature.)

--tml