gh-108985: Make os.DirEntry.is_symlink ~twice as fast

[sobolevn]

Two faster functions are twice as good as one faster function 😄

• Issue: Make os.DirEntry.is_symlink ~twice as fast #108985

[sobolevn]

Oh,

#elif defined(HAVE_DIRENT_D_TYPE)
    /* POSIX */
    if (self->d_type != DT_UNKNOWN)
        return self->d_type == DT_LNK;
    else
        return DirEntry_test_mode(defining_class, self, 0, S_IFLNK);
#else
    /* POSIX without d_type */
    return DirEntry_test_mode(defining_class, self, 0, S_IFLNK);
#endif