The new file names are COPYINGv2 and COPYING.LESSERv2.  Lots of
copyright headers mention COPYING.LIB, so add a symbolic link.
(This is not the first symbolic link in the repository, so this
should be fine.)

The files come from gnulib commit 3cc5b69dda06890929a2d0433f30708.

Signed-off-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Collin Funk <collin.funk1@gmail.com>