zlib refuses to run configure with mingw32 host and insists that
win32/Makefile.gcc is used instead.
This requires a change in this Makefile to support static-only builds.
Fixes#694.
Signed-off-by: Alexey Neyman <stilor@att.net>
The latter does not prevent zlib's configure from overriding 'AR' with
/usr/bin/libtool on macos, and that breaks canadian crosses.
Signed-off-by: Alexey Neyman <stilor@att.net>