I would install build-essentials, compile my stuff, then just copy the output of the compilation in another Docker stage. That’s why we have multi-stage Dockerfiles.
(Or you begin with a more dev/build friendly image and just copy stuff to the minimal hexpm container. That might be an even better idea actually.)
I wouldn’t want to reinvent the minimal images already provided. But if you’re feeling brave and independent, you can always make your own minimal image stepping on e.g. distroless or alpine/wolfie. I personally wouldn’t.
