You should probably only do this `set` if BUILD_THREADS is not defined. Right now you cant configure this outside the script by setting `BUILD_THREADS` before running the deps build, it will always be overwritten by num of processors on the OS. I guess this works if you want to manually go ahead and edit the script on this line.

Also I would make it `TUNDRA_BUILD_THREADS` as `BUILD_THREADS` is quite generic and probably not good to force people to add to their env variables permanently.