[WinEH] Add a funclet layout pass

Windows EH funclets need to be contiguous.  The FuncletLayout pass will
ensure that the funclets are together and begin with a funclet entry MBB.

Differential Revision: http://reviews.llvm.org/D12943

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247937 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed