go: 1.8 -> 1.8.1

[sigma]

Motivation for this change

1.8.1 fixes some issues with MacOS Sierra (golang/go#19734)
as part of this, a fix for golang/go#19772 is bringing to light a bug in the way we invoke dsymutil, which happens to be a stub in darwin cctools (during the build), and generally /usr/bin/dsymutil at runtime.
I'm not entirely sure of the correctness of the fix though, so feedback highly welcome !

I ran nox-review on both MacOS and NixOS, and some compilations failed (like gcsfuse and qsyncthingtray on NixOS, consul, heroku and cadvisor on MacOS) but as far as I can tell are already failing in master.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[mention-bot]

@sigma, thanks for your PR! By analyzing the history of the files in this pull request, we identified @ixmatus, @Mic92 and @LnL7 to be potential reviewers.

[LnL7]

@sigma Have you tried to build this with clang-4, this might be unnecessary now. Otherwise we can probably bump it to 3.9.

[sigma]

@LnL7 yep, clang 4 works too