COMP: fix failing voronoi segmentation tests

Internal comp method used for std::sort didn't induce a strict weak
ordering ( <= vs < ) as required, since it returned true on
equal. This cause failures likely due to difference algorithms in
libc++.

Change-Id: Ic4c8f61d53bce6858b4edcd3a93c605271b0c65b
Merge topic 'FixVoronoiLibc++SortCmp'

b5dd8d4b COMP: fix failing voronoi segmentation tests