Share common ordered comparison code with UN*_EXPR.

Share common ordered comparison code with UN*_EXPR.

Most unordered comparisons can use the result from the ordered
version, if the operands are known not to be NAN or if the result is
true.

gcc/ChangeLog:

	* range-op-float.cc (class foperator_unordered_lt): New.
	(class foperator_relop_unknown): Remove
	(class foperator_unordered_le): New.
	(class foperator_unordered_gt): New.
	(class foperator_unordered_ge): New.
	(class foperator_unordered_equal): New.
	(floating_op_table::floating_op_table): Replace all UN_EXPR
	entries with their appropriate fop_unordered_* counterpart.