Drop support for old configure.ac.
Drop support for old configure.ac.

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