[m-rev.] for post-commit review: detect infinite circular inclusions of options files

[Julien Fischer]

On Sat, 13 Jun 2020, Zoltan Somogyi wrote:

> This would a pretty rare bug to make, but having the compiler
> go into an infinite loop on *any* input should be avoided
> if possible.
>
> For review by Julien, since he should have the relevant info
> in his mental cache.

That looks fine.

Julien.