Update a bunch of loop-vectorize regression tests to use the new PM
syntax (opt -passes=loop-vectorize) instead of the deprecated legacy
PM syntax (opt -loop-vectorize).
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546