With DECC$FILENAME_UNIX_REPORT enabled, all filenames are
    reported in UNIX style unless the caller specifically selects
    OpenVMS style. This applies to getpwnam, getpwuid, argv[0],
    getname, fgetname, and tempnam.

    With DECC$FILENAME_UNIX_REPORT disabled, unless specified in the
    function call, filenames are reported in OpenVMS style.