misc: fix some minor compile warnings all over

Some regarding unused parameter, some regarding signed/unsigned
comparison.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
make: minor update in cflags

Add -z relro for linking, move --param ssp-buffer-size=4 to stack
protector flag, and more.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
make: add HARDENING build option

Add HARDENING=1 build option and move all hardening-related GCC
flags into this condition. This allows the user to choose whether
or not he wants to have a hardened build with some possible performance
tradeoff at load/runtime.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>