The nixpkgs-unstable channel's programs.sqlite was used to identify
packages producing exactly one binary, and these automatically added
to their package definitions wherever possible.
This continues where d8f7f6a5ce left off. Similarly
to that commit, this commit this also points `sourceRoot`s to `src.name` and similar
instead of keeping hardcoded names, and edits other derivation attrs do do the same,
where appropriate.
Also, similarly to d8f7f6a5ce some of expressions this
edits use `srcs` attribute with customly-named sources, so they have to be moved
into `let` blocks to keep evaluation efficient (the other, worse, way to do this
would to recurcively refer to `elemAt n finalAttrs.srcs` or, similarly, with `rec`).
