[m-rev.] for post-commit review: check for du types at the top

[Peter Wang]

On Tue, 21 Jul 2026 17:42:07 +0200 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> For review by Peter.
> 
> Zoltan.
> Lift the test for du types to the top of coercion tests.
> 
> compiler/typecheck_coerce.m:
>     As above.
> 
> compiler/type_assign.m:
>     Generalise an existing kind of coercion failure record
>     to be able to handle the new code in typecheck_coerce.m.
> 
>     Delete a kind coercion failure record that is not needed anymore.
> 
> compiler/typecheck_errors.m:
>     Conform to the changes above.

That looks good.

Peter