I tried that and also

    env CGO_ENABLED=0 go get github.com/google/git-appraise/git-appraise

but I always get an error that go wants to write net.a in /usr/lib, which I naturally am not allowed to do because it's owned by the distro (Arch) go package:

    go install net: open /usr/lib/go/pkg/linux_amd64/net.a: permission denied

I have only set GOPATH to ~/.go and nothing else. Any other GO environment variable I should have used?

Go needs to re-build the stdlib packages with the new build tag as well.

You could install go locally somewhere in ~ and point GOROOT there.