cabal-install-less installation path for Hadrian

Currently Hadrian requires cabal-install or Stack to build Shake, its dependencies, and eventually Hadrian itself.

This may be problematic for commercial users who often need to integrate the GHC build into a larger, often sandboxed, build system.

We will need another option to satisfy this application. I suspect the best option (albeit most involved) is to add a bootstrap script which requires nothing but the bootstrap compiler's Cabal library.