Making the line below a `log.error` instead of `log.info` would make this pull request eligible for merging, right?

I'm fine with doing that and merging it in, since it forces us to properly solve the issue when we run into it for some build.
The fact that the check is missing is a bug imho, which is resolved by this new code.
We know it's possible that the FFTW wrappers are missing, so we should trip over it when they're not there instead of crashing later with confusing `unresolved symbol` problems during linking.

Now, if I only could remember why I even started doing this... ;)