fold-const.c (fold_binary_op_with_conditional_arg): Tweak calling convention to allow...

fold-const.c (fold_binary_op_with_conditional_arg): Tweak calling convention to allow a NULL_TREE to be returned.

	* fold-const.c (fold_binary_op_with_conditional_arg):  Tweak
	calling convention to allow a NULL_TREE to be returned.  Factor
	sanity checks from callers, return NULL_TREE when appropriate.
	(fold): Handle COMPOUND_EXPR operands of binary expressions
	before COND_EXPR operands.  Use reorder_operands_p(a,b) to check
	whether a op (b,c) can be rewritten as (b, a op c).  Simplify
	calls to fold_binary_op_with_conditional_arg.

From-SVN: r80609