fold-const.c (fold): Add constant folding for unordered comparison tree nodes.

	* fold-const.c (fold) <UNORDERED_EXPR, ORDERED_EXPR, UNLT_EXPR,
	UNLE_EXPR, UNGT_EXPR, UNGE_EXPR, UNEQ_EXPR, LTGT_EXPR>: Add
	constant folding for unordered comparison tree nodes.  If both
	operands are real constants, call fold_relational_const.  If either
	operand is a NaN, evaluate the other for side-effects and return a
	constant.  Optimize (double)float1 CMP (double)float2 into the
	equivalent float1 CMP float2.
	(nondestructive_fold_binary_to_constant) <UNORDERED_EXPR,
	ORDERED_EXPR, UNLT_EXPR, UNLE_EXPR, UNGT_EXPR, UNGE_EXPR, UNEQ_EXPR,
	LTGT_EXPR>: Call fold_relational_const for constant operands.
	(fold_relational_const): Add support for unordered comparison tree
	nodes.  Don't constant fold "ordered" floating point comparisons
	against NaN if when flag_trapping_math is set.

	* gcc.dg/unordered-2.c: New test case.
	* gcc.dg/unordered-3.c: New test case.

From-SVN: r83379