The latest release of libyamlcpp in nixpkgs does not build because it
uses an older version of boost than the one in nixpkgs and therefore
expects a particular header file which does not exist in the latest
boost anymore. For this reason, a later (git) version of libyamlcpp is
used here (which actually doesn't even require boost).
The substituteInPlace in the prePatch phase is needed because libevdev
places its headers in non-standard places, meaning Nix cannot normally
find them. The `cut` command removes the first two "-I" characters from
the output of `pkg-config`. This needs to be in the prePatch phase
because otherwise Nix will patch these lines to `/var/empty`, meaning
you would have less specific replacement (in case other lines are also
patched to `/var/empty`).
I wrote the patch. (I believe it is NixOS specific.)
