Because the program doesn't have any binders that -XStrict can make
strict, the desugarer output should be identical when it's compiled with
and without -XStrict. This wasn't the case with GHC 8.2.2, but
apparently it was fixed some time between 8.2.2 and 8.4.1. We now add a
test case to make sure it stays fixed.

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: simonpj, rwbarton, thomie, carter

GHC Trac Issues: #14815

Differential Revision: https://phabricator.haskell.org/D4531