Copy libffi into place
Copy libffi into place

rts needs libffi as libCff in rts/stage1/build. This fixes #89

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