Upstream development has stalled. https://01.org/compute-runtime is the new effort.
Beignet doesn't support CannonLake, IceLake and newer.
This port is a burden during during LLVM_DEFAULT updates. FreeBSD Ports is not upstream thus not a place for abandonware.
A commit references this bug:
Date: Tue Dec 24 08:02:15 UTC 2019
New revision: 520784
lang/beignet: mark as legacy
Intel NEO was added in r519222 while Beignet support stopped at KabyLake.
For one, Beignet doesn't support CoffeeLake and WhiskeyLake but it maybe
possible to patch in unlike IceLake.