You can do this pretty easily using Docker, so no extra libs required. Just run this command:
docker run --rm -it -v "$GOPATH":/go -w /go/src/github.com/iron-io/ironcli golang:1.4.2-cross sh -c '
for GOOS in darwin linux windows; do
for GOARCH in 386 amd64; do
echo "Building $GOOS-$GOARCH"
export GOOS=$GOOS
export GOARCH=$GOARCH
go build -o bin/ironcli-$GOOS-$GOARCH
done
done
'
You can find more details in this post: https://medium.com/iron-io-blog/how-to-cross-compile-go-programs-using-docker-beaa102a316d