Adam Gundry authored Nov 19, 2015 and Ben Gamari committed Nov 19, 2015

This prevents GHC.Generics from exposing mangled selector names
when used on a datatype defined with DuplicateRecordFields enabled.

Test Plan:
New test overloadedrecflds_generics, which tests that both
GHC.Generics and Data.Data use the correct field labels, not mangled
names.

Reviewers: kosmikus, simonpj, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1486