Quick: Fix LoopRepeatingTopologicalSortIterator.

Always push the loop head on the loop head stack. This fixes
a bug where we failed to return to an unnatural loop head to
recalculate its GVN data.

Bug: 17410955

(cherry picked from commit 67c8c942e9dfcabd548351db75e6d3b8b5165afa)

Change-Id: I44b9a17cbcd7307d1cc70ac564b99e29803723c5
3 files changed