compile libcld2 statically

This might be super hacky, and there might be a much nicer way to achieve it. I'd love to see some discussion about what that way might be though, so here I am submitting this pull request.

Basically I just don't want the users of my application to have to download libcld2 and go through the build process, which they would currently have to do, as cld2 doesn't exist in a lot of OS repositories. If there's a better way to do this, I'd love to know it.