Fix layout of MultiWayIf expressions (#10807)

Authored by osa1 on Sep 26 2016, 4:09 PM.

Description

Fix layout of MultiWayIf expressions (Trac #10807)

With this patch we stop generating virtual semicolons in MultiWayIf
guards. Fixes Trac #10807.

Test Plan:

Reviewers: simonmar, austin, bgamari

Reviewed By: simonmar

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2524

GHC Trac Issues: Trac #10807