This commit decouples the MIR printer and the MIR printing pass so
that it will be possible to move the MIR printer into a separate
machine IR library later on.
Reviewers: Duncan P. N. Exon Smith
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239788 91177308-0d34-0410-b5e6-96231b3b80d8