build-sys: add --with-smack to config-gen.d

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: cleanup fix_optstr() regards to selinux and smack

It's better (more robust) to make the code based on datetypes
rather than on if(strcmp(...)).

Signed-off-by: Karel Zak <kzak@redhat.com>