FORTIFY_SOURCE and Safer libc

• -D_FORTIFY_SOURCE=2 (with -O1+) swaps unsafe libc calls for checked variants when a buffer size is known at compile time.
• memcpy → __memcpy_chk, strcpy → __strcpy_chk, sprintf → __sprintf_chk, etc.
• If a copy would exceed the object's known size, the program aborts instead of corrupting memory.
• Also hardens printf against some %n format-string abuses.
• Limits: only when size is statically known; heap objects and truly dynamic sizes are not covered. =3 extends coverage on newer toolchains.