[PredicateInfo] Enable -reverse-iterate tests only for +Asserts builds

Summary: The flag -reverse-iterate is present only on +Asserts builds.

Reviewers: dberlin, davide, RKSimon, efriedma, chapuni

Reviewed By: efriedma, chapuni

Subscribers: chapuni, llvm-commits

Differential Revision: https://reviews.llvm.org/D33795

llvm-svn: 304498