Enable more warnings by default

These are also useful warnings that tend to find real bugs, so let's
enable then.

The downside is they require us to mark certain things so the compiler
knows if they were on purpose or not.

CMakeLists.txt

@@ -73,8 +73,8 @@ ENDIF()
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
 
 # Tell the compiler to be stringent
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wformat=2 -Wvla")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wformat=2 -Wvla")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
 # Make sure we catch these issues whilst developing
 IF(CMAKE_BUILD_TYPE MATCHES Debug)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")