fold-const.c (make_range): Correctly handle cases of converting from unsigned to...

fold-const.c (make_range): Correctly handle cases of converting from unsigned to signed type.

        * fold-const.c (make_range): Correctly handle cases of converting
        from unsigned to signed type.

        * fold-const.c (merge_ranges): Make sure that if one range is subset
        of another, it will always be the second range.  Correct (+,-) case to
        account for this.

Brought over from gcc2; fixes sparc bug.

From-SVN: r15678