[$] GCC features to help harden the kernel

Hardening the Linux kernel is an endless task, with work required on
multiple fronts. Sometimes, that work is not done in the kernel itself;
other tools, including compilers, can have a significant role to play.
At the 2023 GNU Tools
Cauldron, Qing Zhao covered some of the work that has been done in the
GCC compiler to help with the hardening of the kernel — along with work
that still needs to be done.