I just pushed a revamped Go build system with commit
e3900a4d64e4bf6f426809d6bff058e5a2ae9bc8.

The main change is that instead of putting the list of Go-language
dependencies store paths in the GOPATH environment variable, these store
paths are union-symlinked into the build directory, and GOPATH points
there.

This fixes the issue of spurious store references
<https://bugs.gnu.org/33620> and should dramatically reduce the closure
size of certain Go packages. So now there is less reason to use bundled
libraries for Go programs.

I think we should consider another change in how we build Go software:
let's stop splitting up Go libraries instead sub-packages.

For example, the packages 'go-golang-org-x-net-ipv4' and
'go-golang-org-x-net-ipv6' are both from the same Git repo at
<https://go.googlesource.com/net>. We should just package
'go-golang-org-x-net'. It's unidiomatic to split them up. In practice, a
Go programmer would have cloned the Git repo into their Go workspace,
and would never have a "split view" of the x/net libraries.

Thoughts? I can work on this in the next week.