Add -Wno-format-security to build

Some distributions have enabled gcc -Wformat-security by default.
This causes the build to raise format warnings even though -Wformat=0
is used.

Setting no-format-security for build consistency between distros.

Signed-off-by: Or Cohen <orc@fewbytes.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>