With DECC$POSIX_SEEK_STREAM_FILE enabled, positioning beyond
    end-of-file on STREAM files does not write to the file until the
    next write. If the write is beyond the current end-of-file, this
    positions beyond the old end-of-file, and the start position for
    the write is filled with zeros.

    With DECC$POSIX_SEEK_STREAM_FILE disabled, positioning beyond
    end-of-file will immediately write zeros to the file from the
    current end-of-file to the new position.