Oh no problem.
I am running OpenVPN in a container and I need to "customize" it to support MFA. This required building some module from source, hence the need to run a "make".
I understand that Synology does not contain dev tools and we should cross compile. That being said within a container I guess it would be acceptable to build... but I have no idea how to achieve this.
This is one of the cases where "make" allone is insufficient.
You will need to take the Dockerfile of the original Image and enricht the steps you need to compile the modules.
This is far away from beeing a task for a beginner, as you will need to know a) how to edit Dockerfiles (beeing able to read the Dockerfile reference helps a lot), b) how to install the required build chain in the os the base images uses ,c) actualy know the commands to compile the modules and d) know how to integrate it into openvpn (or wherever the target is).