This PR updates the Hydra-generated bootstrap tarballs for
powerpc64le-linux.  The bootstrap-files referenced prior to this
commit will only bootstrap in a nixpkgs which has
#181802.  That PR was closed in
favor of #181943, which is a
cleaner solution but which requires regenerating the bootstrap-files.

I'll be following the script established in
#151399, which I previously used
in #168199.

Files came from [this](https://hydra.nixos.org/build/186237511) Hydra build, which used nixpkgs revision ac43c44 to instantiate:

```
/nix/store/nhjbza9vlcyhp9zxfz6lwpc3m2ghrpzj-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu.drv
```

and then built:

```
/nix/store/fklpm7fy6cp5wz55w0gd8wakyqvzapjx-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu
```

I downloaded these files from Hydra with the following commands:

```
STOREPATH=fklpm7fy6cp5wz55w0gd8wakyqvzapjx-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu
OPTIONS="--option binary-caches https://cache.nixos.org --option trusted-public-keys cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
nix store add-file \
  --name bootstrap-tools.tar.xz  \
  $(nix-store ${OPTIONS} -r /nix/store/${STOREPATH})/on-server/bootstrap-tools.tar.xz
nix store add-path \
  --name busybox \
  $(nix-store ${OPTIONS} -r /nix/store/${STOREPATH})/on-server/busybox
```

I then prefetched them into `/nix/store` with:

```
$ nix store prefetch-file --executable file:///nix/store/p9lz8r81zp3a4sl2qq2v4j69syjzryn2-busybox
Downloaded 'file:///nix/store/p9lz8r81zp3a4sl2qq2v4j69syjzryn2-busybox' to '/nix/store/a42qf2kf5hychcsw5sz0pvghy9vli1im-p9lz8r81zp3a4sl2qq2v4j69syjzryn2-busybox' (hash 'sha256-jtPEAsht4AUAG4MLK8xocQSfveUR4ppU1lS4bGI1VN4=').

$ nix store prefetch-file file:///nix/store/y4530zpk7ia4szf5cdi4zpyy5lpjv3iv-bootstrap-tools.tar.xz
Downloaded 'file:///nix/store/y4530zpk7ia4szf5cdi4zpyy5lpjv3iv-bootstrap-tools.tar.xz' to '/nix/store/kgzyq9q08nll28ccqjcbv8angq5hyvdp-y4530zpk7ia4szf5cdi4zpyy5lpjv3iv-bootstrap-tools.tar.xz' (hash 'sha256-MpIDnpZUK3M17qlnuoxfnK0EgxRosm3TMW1WfPZ1+jU=').
```

And started the bootstrap with the following command:

```
nix build -f . -L hello
```

As @lovesegfault requested in #151399, here are the the `sha256sum`s of all the `on-server` components for extra verification:

```
$ sha256sum /nix/store/fklpm7fy6cp5wz55w0gd8wakyqvzapjx-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu/on-server/*
3292039e96542b7335eea967ba8c5f9cad04831468b26dd3316d567cf675fa35  /nix/store/fklpm7fy6cp5wz55w0gd8wakyqvzapjx-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu/on-server/bootstrap-tools.tar.xz
3d078dff7b4087d82442937667c91dace3321493aae4d3a4160d046b7eabcc2c  /nix/store/fklpm7fy6cp5wz55w0gd8wakyqvzapjx-stdenv-bootstrap-tools-powerpc64le-unknown-linux-gnu/on-server/busybox
```