The SOR$STAT routine returns one statistic about the sort or
    merge operation to your program. You can call the SOR$STAT
    routine at any time while the sort or merge is active.

    Some of the following condition values are used with different
    severities, depending on whether SORT/MERGE can recover. Thus,
    if you want to check for a specific status, you should use
    LIB$MATCH_COND.