Reducing the memory footprint of compiling lib:Cabal

I have been doing some _light_ investigation of what are some of the most consuming modules in `lib:Cabal`, and here are the results based on [time-ghc-modules](https://github.com/codedownio/time-ghc-modules):


I don't really know how to interpret this beyond "Distribution.Simple.Setup should be split in a way that enables multi-core compilation of the package". From a quick glance at this module, there aren't any type-level techniques that would be obviously expensive to compile.

Of course there is a certain number of modules in the package, but I'm positive that expensive compilation is not a fatality.

What do you think?