Pull up following revision(s) (requested by cheusov in ticket #256):
external/gpl2/lvm2/lib/liblvm/Makefile: revision 1.6
external/gpl2/lvm2/sbin/lvm/Makefile: revision 1.11
Add .include <bsd.sys.mk> for initializing USE_SSP.
This fixes build failure if USE_FORT=YES
Approved by christos@