No way to pin build dependencies

[webknjaz (🇺🇦 Sviatoslav Sydorenko (read: /sʋʲɑtɔˈslɑw/))]

I hope that once Add option to include build-system dependencies by apljungquist · Pull Request #1681 · jazzband/pip-tools · GitHub is in, it’ll be easier to generate the pins for this case.