fold-const.c (fold_unary): Don't strip signed nops from ABS_EXPRs.

2005-07-21  James A. Morrison  <phython@gcc.gnu.org>

        * fold-const.c (fold_unary): Don't strip signed nops from ABS_EXPRs.
        (tree_expr_nonnegative_p): Return try for TYPE_UNSIGNED.

From-SVN: r102269