[CMake] Append an option to CMAKE_C_FLAGS_DEBUG

[Mathieu Dubois]

Hello Michael,
> The usual way is to do it just the other way around, and that's also how CMake does it. Instead of defining DEBUG for debug builds, it defines NDEBUG for release builds. So, in your code do:
>
> #ifndef NDEBUG
> printf("THIS IS DEBUG INFORMATION\n");
> #endif
>   
Thank you for the tip... I'll use the standard way.
> Of course, if you insist on DEBUG you can do the following in your top-level CMakeLists.txt file:
>
> set_directory_properties(PROPERTIES COMPILE_DEFINITIONS_DEBUG DEBUG=1)
>   
Nevertheless this is an interesting CMake directive.
> HTH
>   
Yeah it really helped!

Thanks,
Mathieu