Make only install target in libffi.
Make only install target in libffi.

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