[WinEHPrepare] Add rudimentary support for the new EH instructions

[WinEHPrepare] Add rudimentary support for the new EH instructions

This adds somewhat basic preparation functionality including:
- Formation of funclets via coloring basic blocks.
- Cloning of polychromatic blocks to ensure that funclets have unique
  program counters.
- Demotion of values used between different funclets.
- Some amount of cleanup once we have removed predecessors from basic
  blocks.
- Verification that we are left with a CFG that makes some amount of
  sense.

N.B. Arguments and numbering still need to be done.

Differential Revision: http://reviews.llvm.org/D11750

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244558 91177308-0d34-0410-b5e6-96231b3b80d8