CBE: re-introduce bgamari's fixes
CBE: re-introduce bgamari's fixes

During some recent work on CBE we discovered that `zipWith` is used to
check for equality, but that doesn't quite work if lists are of
different lengths! This was fixed by bgamari, but unfortunately the fix
had to be rolled back due to other changes in CBE in
50adbd7c5fe5894d3e6e2a58b353ed07e5f8949d. Since I wanted to have another
look at CBE anyway, we agreed that the first thing to do would be to
re-introduce the fix.

Sadly I don't have any actual test case that would exercise this.

Signed-off-by: Michal Terepeta <michal.terepeta@gmail.com>

Test Plan: ./validate

Reviewers: bgamari, simonmar

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #14226

Differential Revision: https://phabricator.haskell.org/D4387

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc