In #11670 (comment) I discovered that our macOS build job in CI takes ~20 min regardless of how many cores the machine has. Apparently the -j flag we put in MAKEFLAGS variable is getting ignored. I think that the build config generated by CMake on macOS is still make-based so I'm not sure why this is the case.

This needs to be investigated. Once we know how to parallelize it, we should adjust the number of threads/processes and machine resource class in CI for the best cost/benefit ratio.