So for me it wasn't obvious, but when you're running make on the subscribe_publish_sample and getting a ton of warnings and errors like "exit 0" and "exec(exit) failed (No such file or directory)" and "Need an operator" and "Wildcard expanding .prevent_execution" it's because FreeBSD uses a different make than Linux. They use Clang, whereas most Linux Makefiles are written for GCC.

So, what you have to do is explicitly run GNU Make, which is conveniently installed via pkg install gmake and run via gmake.

Voila! Suddenly it works again!