fchmodat.c & lchmod.c - O_PATH & AT_EMPTY_PATH on older kernels

[Lance Fredrickson]

Compiling tar on my embedded device running 2.6.36.4 broke with version 
1.33. Turns out it was a gnulib update they did.

AT_EMPTY_PATH became available in kernel 2.6.39
https://man7.org/linux/man-pages/man2/link.2.html

Here is some discussion
https://github.com/koreader/koreader-base/pull/1288
https://github.com/koreader/koreader/issues/7140

Patch I'm currently using though just a hack and not a true fix.
https://github.com/koreader/koreader-base/blob/master/thirdparty/tar/tar-1.33-remove-o_path-usage.patch

Would be nice to see a fix upstream before more projects update gnulib 
and the issue becomes broader.

thanks,
Lance Fredrickson