Log Message:
If GNU_PROGRAM_PREFIX is empty then conflict with pax package
(which also installs cpio).

This is for my old PR #22693.

(Note I did this different than I did the gtar-base package
which has an another optional setting for choosing the prefix
for gtar which installs gtar with "g" if GNU_PROGRAM_PREFIX is empty.
If that is needed for gcpio also, let me know.)