Ben Gamari authored Jul 19, 2017 and Ben Gamari committed Jul 20, 2017

This flag instructs the simplifier to emit ``error`` expressions in the
continutation of empty case analyses (which should bottom and
consequently not return). This is helpful when debugging demand analysis
bugs which can sometimes manifest as segmentation faults.

Test Plan: Validate

Reviewers: simonpj, austin

Subscribers: niteria, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3736