In reply to @magnetophon:matrix.org
Here's the pkg: https://gist.github.com/magnetophon/86dc90fe4a1e22074e25bccde34e893f
I only changed the src (and one extra lib, but the error already appeared before adding that lib, libXi).

magnetophon i got it

    NIX_CFLAGS_COMPILE = [
      "-I${serd.dev}/include/serd-0"
      "-I${sratom.dev}/include/sratom-0"
      "-I${sord.dev}/include/sord-0"
    ];

you'll see something like this:

 result-dev
├──  include
│   └──  sord-0
│       └──  sord
│           ├──  sord.h
│           └──  sordmm.hpp
├──  lib
│   └──  pkgconfig
│       └──  sord-0.pc
└──  nix-support
    └── 󰡯 propagated-build-inputs