Rik Steenkamp authored Apr 02, 2016 and Ben Gamari committed Apr 04, 2016

Removes the call to `patSynType :: PatSyn -> Type` in `Convert.hs` as this
function will be removed from GHC. Instead, we use the function `patSynSig`
and build the `HsDecl` manually. This also fixes the printing of the two
contexts and the quantified type variables in a pattern synonym type.

Reviewers: goldfire, bgamari, mpickering

Differential Revision: https://phabricator.haskell.org/D2048

(cherry picked from commit 3ddcbd6b)