The notion of "something that shall have been in the language" is not properly defined, as you can basically start from that and arrive at C++. So it is perfect

The notion of "something that shall have been in the language" is not properly defined, as you can basically start from that and arrive at C++. So it is perfectly fine to assume that compile-time programming does not belong into the language and write your own processor. As for DSL, any DSL is a separate language that needs to be learned, so it is not very different from creating your own processor.