[PATCH 1/2] configure: add a fallback check for zlib

[Felipe Contreras]

Xīcò wrote:
> Since zlib is part of the base system, FreeBSD chose not to register it
> in pkg-config through zlib.pc. As a fallback test, configure will build
> and run a zlib version check and make sure the header and library
> versions are compatible.

We could try to generate our on zlib.pc, this way the configure script
would be cleaner.

-- 
Felipe Contreras