packagegroup-core-standalone-sdk-target: add libssp

packagegroup-core-standalone-sdk-target: add libssp

If you want to be able to use -fstack-protector then you need the
runtime support - you can either write this yourself or use libssp
supplied with GCC. If you're using GCC then it seems likely that you'd
just be using libssp, so include in the SDK by default; however use
RRECOMMENDS just in case it's been disabled or you aren't using GCC.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>