[m-rev.] diff: make foreign_import_module an item kind

[Julien Fischer]

On Tue, 29 Jan 2019, Zoltan Somogyi wrote:

> The foreign_import_module pragma is not allowed in source code,
> so it shouldn't be treated as the other pragmas, even though we do use
> pragma syntax to represent them.

The foreign_import_module is very definitely allowed in source code
according to the reference manual.  Changing this requires further
discussion.

Julien.