The previous approach of manually repeating a complex pattern inside Common Lisp
implementation package declarations was fragile and hard to change. After
reading python and lua modules code in Nixpkgs, I was able to come up with
something better.
The function `wrapLisp` doesn't need to be inside package declarations so all
the code for wrapping Lisps can be in `all-packages.nix`.
This works by wrapping the `override` function created from `mkDerivation` to
accept a new argument `packageOverrides`.
One problem with this is that `override.__functionArgs` disappears. But one can
look at the source code of a package to discover what can be overridden.
