- Use the "Fast" flag instead of "OptimizeForSize" to determine whether to emit

  a DBG_LABEL or not. We want to fall back to the original way of emitting debug
  info when we're in -O0/-fast mode.
- Add plumbing in to pass the "Fast" flag to places that need it.
- XFAIL DebugInfo/deaddebuglabel.ll. This is finding 11 labels instead of 8. I
  need to investigate still.

llvm-svn: 65367