[arch-haskell] haskell-haskell-src-exts needs happy to build

Trying to build haskell-src-exts-0.4.6:

Configuring haskell-src-exts-0.4.6... Setup: happy version >=1.17 is required but it could not be found.

Hopefully there would be a way to get cabal2arch to detect that.