hardlink: replace with code from Debian

hardlink: replace with code from Debian

The current version used in util-linux is based on original code from
Jakub Jelinek.

The new version is based on Debian implementation from
https://salsa.debian.org/jak/hardlink.  This new version uses nftw()
to walk on directories tree and organize internal data binary tree
(tsearch() and twalk()). This new version provides more features like
--ignore-{mode,owner,time}, --respect-xattrs, --respect-name,
--include, --keep-oldest, --minimize, --maximize, etc.

Note that the new version uses -f for --respect-name, the old version
uses -f to hardlinking across filesystems (very probably rarely unused
feature).

Addresses: https://github.com/karelzak/util-linux/issues/808
Signed-off-by: Karel Zak <kzak@redhat.com>