Leverage some of the code that John wrote to manage the landing pads.

Leverage some of the code that John wrote to manage the landing pads.

The new EH is more simple in many respects. Mainly, we don't have to worry about
the "llvm.eh.exception" and "llvm.eh.selector" calls being in weird places.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136339 91177308-0d34-0410-b5e6-96231b3b80d8