Possibility to build without zlib

[hestad]

It would be nice to be able to build it without zlib with an option ala. Protobuf:zlib=False

[memsharded]

I have done some initial attempt, but I am having some errors for shared options, because protoc compiler fails. I want to create a fully separated package for protoc, statically linked.

The changes for zlib option are in my branch "feature/updating3.3", in case you want to try them

[hestad]

Thanks, I'll try the changes when I figure how to refer to local conan requires :) Pretty new to the Conan-game.