[PATCH] configure: add workaround for systems without zlib.pc

[David Bremner]

Felipe Contreras <felipe.contreras at gmail.com> writes:

> Some systems (e.g. FreeBSD) might not have installed the appropriate
> pkg-config file as they should. We can workaround the issue by creating
> the .pc file they should have distributed.

I think I agree with Felipe here, this version seems a little easier to
follow. 

d