Build custom predecessor and successor lists for each basic block.

Build custom predecessor and successor lists for each basic block.
These lists exclude invoke unwind edges and loop backedges which
are being ignored. This makes it easier to ignore them
consistently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155500 91177308-0d34-0410-b5e6-96231b3b80d8