We need CallInfoSet to be deterministic because it determines the
order that the binds get generated.

Currently it's not deterministic because it's keyed on
`CallKey = [Maybe Type]` and `Ord CallKey` is implemented
with `cmpType` which is nondeterministic.

See Note [CallInfoSet determinism] for more details.

Test Plan: ./validate

Reviewers: simonpj, bgamari, austin, simonmar

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2242

GHC Trac Issues: #4012