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
Change-Id: I3a2c3225e5d16268c3f56f7f90228759c7da37a9
3 files changed