This is due to the removal of the libmysqld embedded DB server feature in MySQL 8.0.1. I don't have that version here at the moment, but I think I've got it fixed on trunk as of checkin [5767708cd6].

Please try it and let me know if it solves your build issue.

If you'd rather not build from the Fossil trunk, you can just grab the version of lib/options.cpp] and overwrite the release version in the MySQL++ source tree you're trying to build in.