cryptol: fix, rework cryptol 2.6.0 builds

  - The previous build of Cryptol was broken on GHC 8.6.x, which is now the
  new default. That's been fixed with a few upstream patches that will come
  up whenever the next release happens.

  - There was also a build failure on base-compat, fixed by jailbreaking.

  - The previous setup had all-packages.nix creating a new derivation
  solely for the purpose of wrapping the Z3 binary. This has been removed:
  the wrapper is still added but during the Haskell build itself, so that
  all Haskell dependent packages can use the cryptol interpreters too.

  - In its place, we use justStaticExecutables, so people using nix-env
  and Cryptol users who *don't* need haskell dependencies can get much
  smaller closures. Obviously this still implies a second build, but
  this build is much more useful than one that merely adds a shell
  script to a package that's relatively expensive to compile...

Signed-off-by: Austin Seipp <aseipp@pobox.com>