Change range_includes_zero_p argument to a reference.

Change range_includes_zero_p argument to a reference.

Make range_includes_zero_p take an argument instead of a pointer for
consistency in the range-op code.

gcc/ChangeLog:

	* gimple-range-op.cc (cfn_clz::fold_range): Change
	range_includes_zero_p argument to a reference.
	(cfn_ctz::fold_range): Same.
	* range-op.cc (operator_plus::lhs_op1_relation): Same.
	* value-range.h (range_includes_zero_p): Same.