ipa/109983 - (IPA) PTA speedup

This improves the edge avoidance heuristic by re-ordering the
topological sort of the graph to make sure the component with
the ESCAPED node is processed first.  This improves the number
of created edges which directly correlates with the number
of bitmap_ior_into calls from 141447426 to 239596 and the
compile-time from 1083s to 3s.  It also improves the compile-time
for the related PR109143 from 81s to 27s.

I've modernized the topological sorting API on the way as well.

	PR ipa/109983
	PR tree-optimization/109143
	* tree-ssa-structalias.cc (struct topo_info): Remove.
	(init_topo_info): Likewise.
	(free_topo_info): Likewise.
	(compute_topo_order): Simplify API, put the component
	with ESCAPED last so it's processed first.
	(topo_visit): Adjust.
	(solve_graph): Likewise.