Support autogen paths of new Cabal
Support autogen paths of new Cabal

See #269.

izgzhen/hadrian,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,snowleopard/hadrian,snowleopard/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc