Hardened/SSP

For now just some notes:

On gcc-4.9 we will default to strong on non hardened and keep all on hardened. Explain Stack overflow attacks. Explain what the original SSP does, where strong improves and why do we default to all on hardened.

Some links: http://www.outflux.net/blog/archives/2014/01/27/fstack-protector-strong/ http://lwn.net/Articles/584225/