Building a minimal/essential GHC

Dear all, I am working on porting GHC to [native client]( https://developer.chrome.com/native-client), which has some degree of POSIX-compliance. I was thinking about building just the minimal/most essential parts of GHC that is enough to compile simple Haskell programs. I wanted to ask which parts of GHC are the most essential and sufficient enough to compile a simple Haskell program, for instance to compile `main = putStrLn "Hello, world!"`? I also wanted to ask how to force a GHC build without a particular package that comes by default, for instance how to build GHC without the `unix` package? Best wishes, Jakub