fold-const+optabs: Change return type of predicate functions from int to bool

fold-const+optabs: Change return type of predicate functions from int to bool

Also change some internal variables and function argument from int to bool.

gcc/ChangeLog:

	* fold-const.h (multiple_of_p): Change return type from int to bool.
	* fold-const.cc (split_tree): Change negl_p, neg_litp_p,
	neg_conp_p and neg_var_p variables to bool.
	(const_binop): Change sat_p variable to bool.
	(merge_ranges): Change no_overlap variable to bool.
	(extract_muldiv_1): Change same_p variable to bool.
	(tree_swap_operands_p): Update function body for bool return type.
	(fold_truth_andor): Change commutative variable to bool.
	(multiple_of_p): Change return type
	from int to void and adjust function body accordingly.
	* optabs.h (expand_twoval_unop): Change return type from int to bool.
	(expand_twoval_binop): Ditto.
	(can_compare_p): Ditto.
	(have_add2_insn): Ditto.
	(have_addptr3_insn): Ditto.
	(have_sub2_insn): Ditto.
	(have_insn_for): Ditto.
	* optabs.cc (add_equal_note): Ditto.
	(widen_operand): Change no_extend argument from int to bool.
	(expand_binop): Ditto.
	(expand_twoval_unop): Change return type
	from int to void and adjust function body accordingly.
	(expand_twoval_binop): Ditto.
	(can_compare_p): Ditto.
	(have_add2_insn): Ditto.
	(have_addptr3_insn): Ditto.
	(have_sub2_insn): Ditto.
	(have_insn_for): Ditto.