Use zlib if present

[Jeremy Kerr]

Hi Simon,

> This fixes a minor regression that occured with Jeremy's recent
> reworking of the build system. I guess he wasn't dealing with
> compressed images and thus didn't notice that zlib support had
> been disabled.

eep, sorry about that. I wasn't using compressed images.

> The fix involves updating an #ifdef to use the new symbol,
> and ensuring that -lz is passed to the linker as neccessary.

Acked-by: Jeremy Kerr <jk at ozlabs.org>

Cheers,


Jeremy