There are a handful of fsatrace linting errors (missing `need`s) when building libffi. Libffi is ultimately built from a single tar.gz file (e.g. `libffi-tarballs/libffi-3.99999+git20171002+77e130c.tar.gz`). File can be seen as the shallow (file) dependency for the whole libffi build. Hence it should be sufficient to need that file in all libffi rules, and `trackAllow` the whole libffi build directory.