OpenCL on FreeBSD is unusable if we're not proactive in backporting [a regression fix](https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=217635) or [newer llvm support](https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=218644) from upstream. Given no one cared for months let's use a snapshot to avoid disaster on the next update.