Prepare for new pass manager version of `MachineDominatorTreeAnalysis`.
We may need a machine dominator tree version of `DomTreeUpdater` to
handle `SplitCriticalEdge` in some CodeGen passes.
Rename file for PPCCTRLoopsVerify pass from PPCCTRLoops.cpp
to PPCCTRLoopsVerify.cpp.
There will be a new file PPCCTRLoops.cpp for PPC CTR loops
generation later.
