[Loop Predication] Teach LP about reverse loops with uge and sge latch conditions

Add support of uge and sge latch condition to Loop Prediction for
reverse loops.

Reviewers: apilipenko, mkazantsev, sanjoy, anna
Reviewed By: anna
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42837

llvm-svn: 324589