Configure - move the addition of the zlib / libz lib to configs

Configure had the Unix centric addition of -lz when linking with zlib
is enabled, which doesn't work on other platforms.  Therefore, we move
it to the BASE_unix config template and add corresponding ones in the
other BASE_* config templates.  The Windows one is probably incomplete,
but that doesn't matter for the moment, as mk1mf does it's own thing
anyway.

This required making the %withargs table global, so perl snippets in
the configs can use it.

Reviewed-by: Andy Polyakov <appro@openssl.org>