Summary:
The Parser.y production for pquals is

    pquals :: { Located [[LStmt RdrName (LHsExpr RdrName)]] }
        : squals '|' pquals
                         {% addAnnotation (gl $ last $ unLoc $1) AnnVbar (gl $2) >>
                            return (sLL $1 $> (reverse (unLoc $1) : unLoc $3)) }
        | squals         { L (getLoc $1) [reverse (unLoc $1)] }

The squals are returned in reverse order, so the AnnVbar should be
attached to the head of the list, not the last.

Test Plan: ./validate

Reviewers: hvr, austin

Reviewed By: austin

Subscribers: thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D869

GHC Trac Issues: #10357