After cleaning and recompiling everything the error was gone. Mabe there
was an issue with the header file dependencies, so that something that
should have been compiled without cleaning first was not compiled.
Good that it got solved.
My guess is that you had pulseaudio headers, portaudio detected that,
so its build included pulseaudio plugin. Removing PA headers &
re-compiling portaudio removed the asserting plugin from install.
Does that sound plausible?
(I'm asking because there have been other Hatari users who've had assert
issue with pulseaudio plugins when pulseaudio isn't present, and I've
been wondering how they've gotten to that situation.)