Implement ghc/cabal compatiblity matrix (re #415)

This injects lower-bound constraints on Cabal for custom setup
dependencies to prevent the solver from selecting unsupported
configurations.

Previously we already added an absolute lower bound `Cabal >= 1.20`
for nix-local builds, as that's the minimum version we need to be able
to interact with custom Setup.hs scripts. This refines with logic by
restricting that lower bound even more based on GHC version.

This patch augments this with the following rules:

- GHC 8.4+   constrains  Cabal >= 2.2
- GHC 8.2    constrains  Cabal >= 2.0
- GHC 8.0    constrains  Cabal >= 1.24
- GHC 7.10   constrains  Cabal >= 1.22
- (default   constraint  Cabal >= 1.20)

This only affects nix-style local builds codepaths.

(cherry picked from commit 71e797ea)