The version represents the Go version + a counter.
So if the Go version is 1.15.3 and this is the first version based on that:
version=1.15.3 make installmacOS
The macOS part of the build requires the macOS SDK.
To obtain it, register for a developer account, then download Xcode:
Use this page to find links: https://stackoverflow.com/questions/10335747/how-to-download-xcode-dmg-or-xip-file
Or check out crossbuild: https://github.com/multiarch/crossbuild/blob/master/Dockerfile
Using macOS, you can mount the dmg and create the SDK tarfile with create_osx_sdk.sh.
This was taken from here with love: https://github.com/bep/dockerfiles