pillow: Fix build on non-NixOS systems

The Pillow install script will, by default, add paths like /usr/lib and
/usr/include to the search paths.  This can break things when building
on a non-NixOS system that has some libraries installed that are not
installed in Nix (for example, Arch Linux has jpeg2000 but Nix doesn't
build Pillow with this support).

We solve this by telling Pillow to knock it off 😄

Fixes #36317