CMakeLists: Add security flags

Increase security options.

Author: Ricardo Ribalda Delgado <ricardo@ribalda.com>

--- xc3sprog-0+svn795+dfsg.orig/CMakeLists.txt
+++ xc3sprog-0+svn795+dfsg/CMakeLists.txt
@@ -4,7 +4,7 @@ set(xc3sprog_VERSION_MAJOR 0)
 set(xc3sprog_VERSION_MINOR 0)
 
 SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}")
-set(CMAKE_CXX_FLAGS "-g -Wall")
+set(CMAKE_CXX_FLAGS "-g -Wall -O2 -fstack-protector-strong -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2")
 cmake_minimum_required(VERSION 2.6)
 
 find_package(PkgConfig REQUIRED)