media-gfx/slic3r-9999: add missing dep, strip local::lib

local::lib is a workaround to help with the cpan-minus based
build system the package comes with, which we are circumventing
in order to perform a proper system installation.  This commit
includes a patch that reverts the upstream addition of local::lib.

Also adds dev-perl/Devel-CheckLib to the dependency list

Package-Manager: Portage-2.3.8, Repoman-2.3.1