`cp -p' preserves owner/group when the port built by a regular user and
installed by root via SU_CMD.

How-To-Repeat: $ find $(make -V DATADIR) -ls | fgrep -v root
198583       61 drwxr-xr-x   13 holo             holo                  954 Jul  4 06:04 /usr/pkg/share/gnulib/lib
199953        2 -rw-r--r--    1 holo             holo                   27 Jul  4 06:04 /usr/pkg/share/gnulib/lib/posixver.h
199900       12 -rw-r--r--    1 holo             holo                 9805 Jul  4 06:04 /usr/pkg/share/gnulib/lib/gettext.h
200242        4 -rw-r--r--    1 holo             holo                 1709 Jul  4 06:04 /usr/pkg/share/gnulib/lib/dummy.c
199904       27 -rw-r--r--    1 holo             holo                36634 Jul  4 06:04 /usr/pkg/share/gnulib/lib/gl_list.h
199483        4 -rw-r--r--    1 holo             holo                 2035 Jul  4 06:04 /usr/pkg/share/gnulib/lib/gl_linked_list.c
199956        2 -rw-r--r--    1 holo             holo                  212 Jul  4 06:04 /usr/pkg/share/gnulib/lib/userspec.h
199486        5 -rw-r--r--    1 holo             holo                 2865 Jul  4 06:04 /usr/pkg/share/gnulib/lib/gc-pbkdf2-sha1.c
199926       47 -rw-r--r--    1 holo             holo                38056 Jul  4 06:04 /usr/pkg/share/gnulib/lib/hash.c
...

$ gnulib-tool --update (on this repo - http://github.com/wrp/wscreen/tree/wrp )
Module list with included dependencies (indented):
    alignof
    alloca
    alloca-opt
...
File list:
  build-aux/arg-nonnull.h
  build-aux/c++defs.h
...
Creating directory ./lib
Creating directory ./build-aux
/usr/pkg/bin/gnulib-tool: *** file /usr/pkg/share/gnulib/top/GNUmakefile not found
/usr/pkg/bin/gnulib-tool: *** Stop.