cc/gcc: add an option to enable/disable build of libssp

libssp is the run-time Stack-Smashing Protection library.
It can be usefull to have or miss, depends...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Julien DUSSER"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00054.html"

 reporter_comment="Soft-float for the 405 PowerPC"