Enable _FORTIFY_SOURCE=3 for gcc 12 and above

gcc 12 now has support for the __builtin_dynamic_object_size builtin.
Adapt the macro checks to enable _FORTIFY_SOURCE=3 on gcc 12 and above.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>