[RFA] Add support for --without-zlib (take 2)

[Tom Tromey]

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> Tom: I tried to think about how to integrate ourselves better with
Joel> GCC's configure option (--with-system-zlib), but I couldn't think
Joel> of anything nice.

Thanks for looking.

Joel> I think GCC should have implemented optional in-tree support the
Joel> way you did for iconv.

The situations aren't totally analogous.  zlib is always in the gcc
tree, and for gcj (and now I think, LTO), it is not an optional
dependency.

Tom