vm/windows: Make list of dependencies explicit.

So far, the VMs have always been using the native architecture, because
it was reimporting <nixpkgs> several times. Now, we propagate a list of
packages down to all sub-imports, which not only makes clearer which
dependencies a part actually has, but also will make it easier in case
we want to refactor those parts to use callPackage.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>