The CONTRIBUTING.md requests an (or multiple) SPDX identifier for GPL
licenses. But a lot of packages did use a different, non-SPDX style with a
"+" at the end instead of "-or-later".

Signed-off-by: Sven Eckelmann <sven@narfation.org>

Required by Authen::SASL to have actual plug-ins to handle the
protocol.

Uses Devel::CheckLib which doesn't work with cross-compilation with
the current perlmod.mk machinery.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>