Apologies, scratch that last backtrace, I had not rebuilt everything sufficiently diligently!
The version of antlr3c in the linphone branch of your repository allows me to build a working (well, not crashing on startup, I haven't done any further testing yet) version of linphone! Thanks for the pointer :)
Next question: is there a solid tag which I can check out in that repository, rather than the moving target which is the head of the linphone branch? I'd definitely rather not check out a moving target in the portfile since it's bad for reproducibility!