[m-rev.] for post-commit review: start on diagnostic for missing interface files

[Zoltan Somogyi]

On Sun, 5 Jul 2026 15:13:00 +1000, Julien Fischer <jfischer at opturion.com> wrote:
> We could just look to see if intermodule optimization has been enabled by
> the user and only include that part of the message if it is.

I thought about it, but I think it is better to give the full story in one diagnostic.
mainly because I dont' think users should need to wait until they enable --intermod-opt
to be told about .opt files needing to be built beforehand.

I followed all your other suggestions.

Zoltan.