- Now correctly sets NIX_GHC* env vars

(cherry picked from commit 84e915a)

Usuage: Add breakpointHook to your `buildInputs` like this:

  stdenv.mkDerivation rec {
    # ...
    buildInputs = [ breakpointHook ];
  });

When the build fails as show in this example:

  pkgs.hello.overrideAttrs (old: {
    buildInputs = [ breakpointHook ];
    postPatch = ''
      false
    '';
  });

It will halt execution printing the following message:

build failed in patchPhase with exit code 1
To attach to this build run the following command as root:

   cntr attach -t command cntr-/nix/store/ynyb4n82x2r7sldd58pbb405jdqh5f00-hello-2.10

Installing cntr and running the command will provide shell access to the
build sandbox of failed build:

sudo cntr attach -t command cntr-/nix/store/ynyb4n82x2r7sldd58pbb405jdqh5f00-hello-2.10
WARNING: bad ownership on /nix/var/nix/profiles/per-user/root, should be 1000
[nixbld@localhost:/var/lib/cntr]$

At /var/lib/cntr the sandbox filesystem is mounted. All commands and
files of the system are still accessible within the shell.
To execute commands from the sandbox use the `cntr exec` subcommand.

(cherry picked from commit f10b935)

(cherry picked from commit 325a569)

(cherry picked from commit 7f80fb2)

Backport breakpointHook [18.09]

(cherry picked from commit a88e0ef)

[18.09] nixos/trezord: revised and updated udev rules

This replaces standard checkPhase using setup.py that uses pytest-runner
with an explicit call to pytest. One reason to do that is because
setup.py triggers another rebuild when asked to do "test". Another
reason is that there seems to be a conflict between possible imports for
pyarrow: `pwd`/pyarrow vs $out/pyarrow. By some unknown reason this
triggers an import error on hydra and ofborg, but not on my machine. The
solution here is to remove `pwd`/pyarrow, keep the tests and use direct
call to pytest (setup.py needs `pwd`/pyarrow). The added benefit is that
we are now testing what is installed in $out.

(cherry picked from commit 6ae3cb4)

Backport #46453