Working on a v6 for this, Efraim pointed out to me that a lot
of the intermediate packages arent building as-is after
removing all the `skip-build? #t`. v6 will address that, and
should be done in the next day or so. 

So far the only package particularly egregious to get a
decent method of building + testing is `rust-diffus` + its
derive macro crate (upstream is <https://github.com/distil/diffus/tree/master>).
Any help/advice on that one would be great as:

- they both reference a README that is in a parent directory
  - easy enough and is worked around to build the
    `diffus` crate proper.
- the derive macro is in a workspace, and no incantation
  of `--exclude`  / `--manifest-path` etc will only build the
  `-derive` without the `diffus` proper.

For now I just have the `rust-diffus-derive` package
marked as `#:skip-build? #t`.

- Jordan