I don't think the fork API conflict with the libpthread API. It should be possible to have both in "heavy." There are a few packages that use libunbound as a helper so I want "heavy" to be base+plus rather than mutually exclusive. I am investigating a patch to remove or change the conditional compile.
never mind: threads are simulated with forks using macro wrappers in headers with conditional compile. Thoughts, why wouldn't a library API be a linkable function with all the options twist under the hood of the library.