This tracks down to a bug/missing bit in the latest FLTK 1.3.6, where linking of remote.o fails to find fl_wait() for the Mac/Cocoa platform.
https://github.com/fltk/fltk/issues/246
I've filed a ticket upstream and will stay on it, but curious if anyone else is in there and/or has been working on this.
Of course I notice this after I post... I just cloned the Git repository as opposed to downloading the latest source here on SF and it builds & runs just fine. So this may be a non-issue.