gimple-ssa-evrp.c (evrp_dom_walker): Add cleanup method.

	* gimple-ssa-evrp.c (evrp_dom_walker): Add cleanup method.
	Add private copy constructor and move assignment operators.
	Privatize methods and class data where trivially possible.
	(evrp_dom_walker::cleanup): New function, extracted from
	execute_early_vrp.  Simplify access to class data.

From-SVN: r254882