Name resolution failures during build

[Stephen Scheck]

I'm getting the following error when I try to install a package I'm working
on:

    go: github.com/BurntSushi/toml@v0.3.1: Get "
https://proxy.golang.org/github.com/%21burnt%21sushi/toml/@v/v0.3.1.mod":
dial tcp: lookup proxy.golang.org on [::1]:53: read udp
[::1]:43973->[::1]:53: read: connection refused

It uses `gnu-build-system`. Is there some package that needs to be added to
the build inputs for ordinary name resolution to work?