ART: Update last_instruction when adding Phis

HBasicBlock::InsertPhiAfter would not update the last_instruction
pointer when adding at the end of the list. This could cause problems
when iterating over phis backwards. Fortunately, we don't do that
anywhere in the existing code.

Change-Id: I4487265bf2cf3d3819623fafd7ce7c359bac190e
3 files changed