[PowerPC] Turn on CR-Logical reducer pass

This re-commits r375152 which was pulled in r375233 because it broke
the EXPENSIVE_CHECKS bot on Windows.

The reason for the failure was a bug in the pass that the commit turned
on by default. This patch fixes that bug and turns the pass back on.
This patch has been verified on the buildbot that originally failed
thanks to Simon Pilgrim.

Differential revision: https://reviews.llvm.org/D52431

llvm-svn: 375497