[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.
>
> Signed-off-by: Felipe Contreras <felipe.contreras at gmail.com>

pushed to release and master

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