Merging r182485:
------------------------------------------------------------------------
r182485 | arnolds | 2013-05-22 09:54:56 -0700 (Wed, 22 May 2013) | 7 lines

LoopVectorize: Make Value pointers that could be RAUW'ed a VH

The Value pointers we store in the induction variable list can be RAUW'ed by a
call to SCEVExpander::expandCodeFor, use a TrackingVH instead. Do the same thing
in some other places where we store pointers that could potentially be RAUW'ed.

Fixes PR16073.
------------------------------------------------------------------------