increase security/safety checks for SSP and FORTIFY

[netchild]

Summary

SSP:
add stack clash protection, see

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
https://developers.redhat.com/blog/2020/05/22/stack-clash-mitigation-in-gcc-part-3
https://blog.llvm.org/posts/2021-01-05-stack-clash-protection/

FORTIFY:
add some compile time checks for arrays, see

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html

Test Plan

All of this runs since some months on a jail host with mysql, postgresql,
redis, named, unbound, openldap, postfix, rspamd, dovecot, php 8.3,
python, various java based services, squid, nginx, samba, ...