Split TailDuplicatePass into pre- and post-RA variant; NFC

Split TailDuplicatePass into EarlyTailDuplicate and TailDuplicate. This
avoids playing games with fake pass IDs and using MRI::isSSA() to
determine pre-/post-RA state.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322926 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed