--reproducible does not make the c_nlink count deterministic

[Elias Naur]

Hi,

I'm using cpio to generate initramfs images that must be bit-for-bit
reproducible regardless of the build platform. However, the
--reproducible flag does not apply to the hard link count stored in
the c_nlink header value[0]. As is, the count depends on the
underlying filesystem and is thus not deterministic.

My specific problem is hard link counts differing between darwin and
ext4 filesystems, but it seems to me the hard link counts may differ
on other filesystems too[1].

Elias

[0] https://git.savannah.gnu.org/cgit/cpio.git/tree/src/util.c#n1136
[1] https://www.spinics.net/lists/linux-btrfs/msg98964.html