Try adding support for combining cargo auditable with cargo-zigbuild/xwin

We currently error out on trying the combination of `cargo auditable` with `cargo zigbuild`/`cargo xwin`, because they're all subcommands. However, according to https://github.com/rust-secure-code/cargo-auditable/issues/167, it looks like this combo might actually be possible so long as `auditable` comes first in the argument list. I'll test this and see if I can confirm.