Some years back I built and got working on a beagle bone black gforth and
serial port for programming SiLab boards. I believe it works on the PI as well.
You can find a tar version of the source tree - I think it was 7.9 at the time,
on my web site. There is also an article discussing some minor points of
doing the compile - might be more articles as well.
Try:
http://www.kiblerelectronics.com/kibler/gforth_armhf.tar
The old article is:
http://www.kiblerelectronics.com/corner/ccii_27.html
Please note - that there was a time when the serial action was somewhat broke,
but all new versions of the code should work. Some of the myforth articles might
help as myforth uses gforth to talk and program the SiLab boards.
Hope this helps.
Bill.