Update edge weights correctly in replaceSuccessor().

When replacing Old with New, it can happen that New is already a
successor. Add the old and new edge weights instead of creating a
duplicate edge.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161653 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed