GCC: Add a new option "-fstack-protector-strong"

This includes additional functions to be protected: those that
have local array definitions, or have references to local frame
addresses. This is a new option in GCC-4.9 that was relicensed
by Han Shen from Google under GPLv2 for OpenBSD.

Obtained from: OpenBSD (2014-01-14)
MFC after: 2 weeks