Scons now doesn't throw away /home/stewart/.nix-profile/lib/pkgconfig:/nix/var/nix/profiles/default/lib/pkgconfig:/run/current-system/sw/lib/pkgconfig, so NixOS can build it
Merge pull request #107 from sjmackenzie/master

Scons now doesn't throw away PKG_CONFIG_PATH, so NixOS can build it