Those issues are the same as I encountered and led up to the Docker file for Ubuntu 16.04 that I posted above, even though libltdl-dev was implicitly included by something else, so I didn’t have that problem.
This again raises the question how our build system is supposed to work. I would’ve expected that it shouldn’t complain about missing things that it has already detected it cannot build.
My expectation would be that this was done automatically per above, not that a hack for each operating system should be necessary. That could also have negative consequences. Suppose a user has an Ubuntu 16.04 system with ocaml included, they would be prohibited to build with ocaml by the rule modification you suggest.
Sorry if I have misunderstood something. In that case, please educate me.