refs #583 - report `CACHE_ERROR` when `simplecpp::FileDataCache::getFileId()` fails by firewave · Pull Request #587 · cppcheck-opensource/simplecpp

I chose a different type so we not need to pipe the more verbose information from the generic missing include error.

The idea for hooking this up in Cppcheck would be to report this with --verbose or --check-config only.

It might make sense to cache it from CACHE_ERROR to some more generic as CACHE_MSG so we could pass on some information about the cache (like statistics). Introducing an additional list within the cache object would add more complexity to the integration.