Create a fast VRP pass

Create a fast VRP pass

	* timevar.def (TV_TREE_FAST_VRP): New.
	* tree-pass.h (make_pass_fast_vrp): New prototype.
	* tree-vrp.cc (class fvrp_folder): New.
	(fvrp_folder::fvrp_folder): New.
	(fvrp_folder::~fvrp_folder): New.
	(fvrp_folder::value_of_expr): New.
	(fvrp_folder::value_on_edge): New.
	(fvrp_folder::value_of_stmt): New.
	(fvrp_folder::pre_fold_bb): New.
	(fvrp_folder::post_fold_bb): New.
	(fvrp_folder::pre_fold_stmt): New.
	(fvrp_folder::fold_stmt): New.
	(execute_fast_vrp): New.
	(pass_data_fast_vrp): New.
	(pass_vrp:execute): Check for fast VRP pass.
	(make_pass_fast_vrp): New.