re PR tree-optimization/23942 (loop problem / testcase takes very long time to compile)

	PR tree-optimization/23942
	* Makefile.in (SCEV_H): Depends on PARAMS_H.
	* tree-scalar-evolution.c: Include params.h.
	(t_bool): New enum.
	(follow_ssa_edge, follow_ssa_edge_in_rhs,
	follow_ssa_edge_in_condition_phi_branch,
	follow_ssa_edge_in_condition_phi, follow_ssa_edge_inner_loop_phi):
	Change return type to t_bool.  Use a parameter to limit the size of
	trees that are walked before stopping
	(analyze_evolution_in_loop): Initialize the limit to 0.
	(follow_ssa_edge): Give up by returning t_dont_know if the limit
	exceeds PARAM_SCEV_MAX_EXPR_SIZE.

From-SVN: r104653