fold-const.c (split_tree): Add MINUS_LITP parameter; separate added literals from substracted literals.

        * fold-const.c (split_tree): Add MINUS_LITP parameter; separate
        added literals from substracted literals.
        (associate_trees): Don't convert MINUS_EXPR into PLUS_EXPR.
        (fold) [associate]: Preserve MINUS_EXPR if needed.

	* gcc.c-torture/execute/20020423-1.c: New.

From-SVN: r52695