Fix space leaks in simplifier (#13426)

Authored by rwbarton on Mar 31 2017, 10:37 AM.

Description

Fix space leaks in simplifier (Trac #13426)

The Join points commit (8d5cf8bf) introduced a space leak
somewhere in the simplifier. The extra strictness added in this commit
fixes the leak. Unfortunately I don't really understand the details.

Unfortunately, the extra strictness appears to result in more overall
allocations in some cases, even while the peak heap size decreases in others.

Test Plan: harbormaster

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3399