Compositor: Enable suggest-override warning.

Compostior relies heavilly on overridden methods. The override keyword has been added
in this module and is desired. The benefit of the override keyword is
that it reports an error when not applied to a (base) virtual method and report
what will not match when refactoring the code to be closer to blender style guide.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D10846

source/blender/compositor/CMakeLists.txt

@@ -608,4 +608,8 @@ endif()
 
 blender_add_lib(bf_compositor "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 
+if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
+  target_compile_options(bf_compositor PRIVATE "-Wsuggest-override")
+endif()
+
 add_dependencies(bf_compositor smaa_areatex_header)