After updating value handles for RAUW, check that no weak or tracking handles

After updating value handles for RAUW, check that no weak or tracking handles
are still on the list.  This might happen if a CallbackVH created some new value
handles for the old value when doing RAUW.  Barf if it occurs, since it is almost
certainly a mistake.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109495 91177308-0d34-0410-b5e6-96231b3b80d8