cmake: enable extra compiler checks

Let's enforce additional automatic checks enforced by the compiler in
order to catch possible errors during compilation.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

CMakeLists.txt

@@ -3,7 +3,12 @@ cmake_minimum_required(VERSION 2.6)
 INCLUDE(CheckIncludeFiles)
 
 PROJECT(uclient C)
-ADD_DEFINITIONS(-Os -Wall -Werror --std=gnu99 -g3 -Wmissing-declarations)
+ADD_DEFINITIONS(-Os -Wall -Werror --std=gnu99 -g3)
+IF(CMAKE_C_COMPILER_VERSION VERSION_GREATER 6)
+        ADD_DEFINITIONS(-Wextra -Werror=implicit-function-declaration)
+        ADD_DEFINITIONS(-Wformat -Werror=format-security -Werror=format-nonliteral)
+ENDIF()
+ADD_DEFINITIONS(-Wno-unused-parameter -Wmissing-declarations)
 
 SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")