Are you building a v28 tag, latest master or one of the v29 release tags?
Discussion
I'm actually trying the build sjors' Sv2 branch: https://github.com/sjors/bitcoin
I think the next step is to try to build outside of nix. But I have to put this down and get some stuff done today. Time waits for no build error.
That's slightly behind v29 (not far) but I suggest trying master first.