Fix a post-RA scheduling liveness bug. When a basic block is being

scheduled in multiple regions, liveness data used by the
anti-dependence breaker is carried from one region to the next, however
the information reflects the state of the instructions before scheduling.
After scheduling, there may be new live range overlaps. Handle this by
pessimizing the liveness data carried between regions to the point where
it will be conservatively correct now matter how the earlier region is
scheduled. This fixes a miscompilation in 176.gcc with the post-RA
scheduler enabled.

llvm-svn: 66558