haskell.packages.ghcjs: fix entropy (#20446)

  # https://github.com/haskell/haddock/issues/553

  wai = dontHaddock super.wai;

  cereal = addBuildDepend super.cereal [ self.fail ];

  entropy = overrideCabal super.entropy (old: {

    postPatch = old.postPatch or "" + ''

      # cabal doesn’t find ghc in this script, since it’s in the bootPkgs

      sed -e '/Simple.Program/a import Distribution.Simple.Program.Types' \

          -e 's|mConf.*=.*$|mConf = Just $ simpleConfiguredProgram "ghc" (FoundOnSystem "${self.ghc.bootPkgs.ghc}/bin/ghc")|g' -i Setup.hs

    '';

  });

}