[$] Two security improvements for GCC

It has often been said that the competition between the GCC and LLVMcompilers is good for both of them. One place where that competition shows up is in the area of security features; if one compiler adds a way toharden programs, the other is likely to follow suit. QingZhao's session at the 2021Linux Plumbers Conference told the story of how GCC successfully playedcatch-up for two security-related features that were of special interest tothe kernel community.