Support cross with -tags pkcs11

Apparently the OSX client needs `-tags pkcs11` (something about working with yubikey).

Using that tag fails with compilation errors. I believe this is because `CGO_ENABLED=0` is set. 

There's also this section from the moby/moby Dockerfile which we might need: https://github.com/moby/moby/blob/bf5cf84534f1eac9805c6f1bffff341358806b57/Dockerfile#L100-L109