Well I know macbooks (and they could be recognized as such during an install) are notorious B43 machines but actually wondering if there are stil that many USB versions around. 
How often would that be a problem, for it to have this non-free binary blob contaminating the kernel?
Maybe just leave it out until it gets fixed for 5.4 (and later) ?
Never mind .... I just discovered that the source of said broadcom-sta-dkms package was added which allows for succesful compilation. 
Nicely solved. 
