Mark all the _REV instructions as not having side effects. They aren't really emitted...

Mark all the _REV instructions as not having side effects. They aren't really emitted by the backend, but it reduces the number of instructions in the output files with unmodelled side effects to make auditing easier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171118 91177308-0d34-0410-b5e6-96231b3b80d8