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 +3,7 @@ INCLUDE(CheckLibraryExists)
 INCLUDE(CheckFunctionExists)
 
 PROJECT(ubox C)
-ADD_DEFINITIONS(-Os -Wall -Werror --std=gnu99 -g3 -Wmissing-declarations)
+ADD_DEFINITIONS(-Os -Wextra -Wall -Werror --std=gnu99 -g3 -Wmissing-declarations -Wno-unused-parameter)
 
 OPTION(BUILD_LUA "build Lua plugin" ON)
 OPTION(BUILD_EXAMPLES "build examples" ON)