Now that multiple DAGUpdateListeners can be active at the same time,
ISelPosition can become a local variable in DoInstructionSelection.
We simply register an ISelUpdater with CurDAG while ISelPosition exists.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155249 91177308-0d34-0410-b5e6-96231b3b80d8