[PATCH] DataFlowSanitizer: Make unreachable BBs verify under the args ABI.

[Evgeniy Stepanov]

  See what we did in MSan for this:
  http://llvm-reviews.chandlerc.com/D208
  http://llvm-reviews.chandlerc.com/D208

  Seems like the new function in Utils might have evolved from something simple to be almost equivalent to the one in SimplyCFG.

http://llvm-reviews.chandlerc.com/D1316