Were you able to get llvm overridden I’m trying to do something similar but with this fork. I tried all sorts of things including this fork of nixpkgs. No matter what I try it builds the original llvm (if I override llvmPackages_21 it’s clang 21, if I try llvmPackages_git it’ll be what’s in the git version, currently 22.0.0). The changes and flake I’m trying to do this in is here