GOOS and GOARCH being set like this makes it impossible to compile on
other archs.
For me GOARCH prevents compilation on my ARM machine.
For others GOOS will prevent windows.
xref https://github.com/rclone/rclone/issues/4086
* Use a multi-stage build to reduce final image size.
* Run 'quicktest' make target before building.
* Built binary won't run on Alpine unless statically linked.
