[Bug fortran/85407] Replace gcc_assert in module.c:read_module by more helpful diagnostics

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85407

--- Comment #2 from Harald Anlauf <anlauf at gmx dot de> ---
(In reply to Dominique d'Humieres from comment #1)
> The trunk is now at 9.0. The patch can be committed if accepted.

It was my understanding that Steve OK'd it and said that he'd commit,
but then did not.

I do not have commit rights.