unmark_used_attributes, add_values_to_cover, increment_current_value,
	test_for_current_value, simplify_with_current_value,
	simplify_with_current_value_aux): New functions.
	(struct function_unit): Add max_busy_cost, {min,max}_busy_delay.
	(expand_units): Use simplify_by_exploding to simplify the
	function_units_used attribute.  Compute the ready cost attributes
	as a COND in numeric order.
	(gen_unit): Compute {min,max}_ready_cost and {min,max}_busy_delay.
	(write_function_unit_info): Determine if there is only one busy
	delay value by comparing the minimum and maximum busy delay.
	Write the initializer for function_units in numeric order.
	Write out the maximum busy delay field.

(attr_desc): Add negative_ok field.
	(find_attr, make_internal_attr): Initialize negative_ok.
	(check_attr_value): Allow negative values for CONST_STRING for
	numeric attributes with negative_ok.
	(encode_units_mask): Change the encoding of the function_units_used
	result.

{....

From-SVN: r1848