Refactor the Graph writing code to use a common implementation which is
now in lib/Support/GraphWriter.cpp. This completes the PR.
Patch by Anton Korobeynikov. Thanks, Anton!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28925 91177308-0d34-0410-b5e6-96231b3b80d8