Update haskell-mode recipe to build autoloads file

"haskell-site-file.el" was recently [removed](https://github.com/haskell/haskell-mode/commit/ae7cee055775c37fc24ed90088aca4445df042b0) from  [haskell-mode repository](https://github.com/haskell/haskell-mode), explicit :build step is now needed for recipe to work