Fix another batch of `./validate --slow` failures

A rather detailed summary can be found at:

    https://gist.github.com/alpmestan/be82b47bb88b7dc9ff84105af9b1bb82

This doesn't fix all expectation mismatches yet, but we're down to about
20 mismatches with my previous patch and this one, as opposed to ~150
when I got started.

Test Plan: ./validate --slow

Reviewers: bgamari, erikd, simonmar

Reviewed By: simonmar

Subscribers: thomie, carter

GHC Trac Issues: #14890

Differential Revision: https://phabricator.haskell.org/D4636