It turns out, that some people have issues with the compiler auto-detection in 20.03. This article should help:
http://forums.next.codeblocks.org/index.php/topic,23738.msg161976.html#msg161976
Also, please have a look here:
http://forums.next.codeblocks.org/index.php/topic,23724.msg161923.html#msg161923