Don't suggest deprecated flags in error messages

Authored by MartinCeresa on Oct 7 2016, 7:54 AM.

Description

Don't suggest deprecated flags in error messages

When looking up flags, we make sure to lookup the non-deprecated flags first
by ordering the list of flags.

Reviewers: bgamari, austin, mpickering

Reviewed By: mpickering

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2541

GHC Trac Issues: Trac #12574