niteria authored Aug 31, 2015 and Simon Marlow committed Aug 31, 2015

Summary:
This is very similar to D1073. It makes type family instances to be
attached to a binding with a least `OccName`, therefore not depending on `Unique` ordering.

Test Plan:
* this makes `Language.Haskell.Exts.SrcLoc` deterministic
* ./validate

Reviewers: simonmar, austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1192

GHC Trac Issues: #4012