Use Quickest flavour on Mac OSX
Use Quickest flavour on Mac OSX

See #259

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