bin/lib/cygbuild.pl: update to xz
Update find(1) option -perm

Signed-off-by: Jari Aalto <jari.aalto@cante.net>
bin/lib/cygbuild.pl: (HELP::OPTIONAL EXTERNAL FILES): Document delete.lst

Signed-off-by: Jari Aalto <jari.aalto@cante.net>