I've had this annoyance for a while building from a clean tree on macOS Steps to reproduce: ``` % ./boot % ./configure % ./hadrian/build -j ``` The build fails building `ghc-prim` with a missing `ffi.h` error. The quickest way to do a full build is: ``` % ./hadrian/build -j # wait until failure % ./hadrian/build ^C # (after libffi/rts have been built completely) % ./hadrian/build -j # wait until build finishes ``` Perhaps the failure depends on the number of jobs, it fails reliably on my 12-core M2 Max CPU.