build: treat warnings as errors

CMakeLists.txt

@@ -8,6 +8,8 @@ if (WIN32)
     "<CMAKE_RC_COMPILER> <FLAGS> -O coff <DEFINES> -i <SOURCE> -o <OBJECT>")
 endif ()
 
+set(CMAKE_COMPILE_WARNING_AS_ERROR ON)
+
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/bin)
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/lib)
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/lib)