go_bootstrap: remove top-level attribute

[zowoq]

Motivation for this change

Fixes #110794

Closes #73643
Closes #88315
Closes #93989
Closes #96786
Closes #99778
Closes #106194
Closes #106195
Closes #109174
Closes #109175

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

cc @NixOS/golang

[zowoq]

@ofborg build go_1_14 go_1_15 podman

[kalbasit]

🎉

[bobrik]

This file is still not accessible if not for cache.nixos.org:

* SSL: no alternative certificate subject name matches target host name 'cache.xor.us'

It also doesn't feel very trustworthy.

How do you feel about bootstrapping from golang.org binary packages repackaged to look like bootstrap? I have the following for aarch64-darwin locally:

      (srcOnly {
        name = "go-1.16-rc1-darwin-arm64-bootstrap";
        src = fetchurl {
          url = "https://golang.org/dl/go1.16rc1.darwin-arm64.tar.gz";
          sha256 = "1p9l9qrh5x06jw19bnyfz8hfq6fisxzhc39cq6gwg4xcvn7gxq7m";
        };
      }).overrideAttrs (_: rec {
        installPhase = ''
          mkdir -p $out/share/go $out/bin
          mv bin/* $out/bin
          cp -r . $out/share/go
        '';
      })

Same idea would apply to aarch64-linux here, or to any arch that cannot be bootstrapped from go1.4.

[kalbasit]

This was partially discussed in #110794, IMO please open a new issue so we can discuss it. Personally, I think it would be fine.