Indeed, the FAST_LOCK is not defined on MacOS when compiling using the old Makefiles. I guess it has to be as an option and decide based on cpu/arch to use it or not.
Ultimately MacOS is not a primary target for server side, but afaik it is similar with many *BSDs, and some people were using K on *BSD along the time. That's why I tried again on MacOS to see how it goes.