Makefiles/automake isn’t a reasonable expectation these days, with a plethora of languages and build toolchains, but good, clear instructions are definitely something to include.
As for the Makefiles, I meant that for whatever build toolchain the project uses - because the rules to build a project are an essential part of the project, linking the source code into a working library or executable. Whether it is cmake, or gnu make, or whatever else there is - that's not so important as long as those build toolchains are available cross platforms.
I think what is really missing in the open source world is a distribution-agnostic standard how to describe application dependencies so that package maintainers can auto-generate distro-packages with the distribution-specific dependencies based on that "dependencies" file.
Similar to debian dependencies Depends: libstdc++6 (>= 10.2.1)
but in a way that identifies code modules, not packages, so that distributions that package software together differently will still be able to identy findPackageFor( dependency )
I would really like to add this kind of info to my projects and have a tool that can auto-build a repo-package from those.