tree-optimization/116002 - PTA solving slow with degenerate graph

tree-optimization/116002 - PTA solving slow with degenerate graph

When the constraint graph consists of N nodes with only complex
constraints and no copy edges we have to be lucky to arrive at
a constraint solving order that requires the optimal number of
iterations.  What happens in the testcase is that we bottle-neck
on computing the visitation order but propagate changes only
very slowly.  Luckily the testcase complex constraints are
all copy-with-offset and those do provide a way to order
visitation.  The following adds this which reduces the iteration
count to one.

	PR tree-optimization/116002
	* tree-ssa-structalias.cc (topo_visit): Also consider
	SCALAR = SCALAR complex constraints as edges.