autoconf itself doesn't need xz, but in Nixpkgs xz is part of the stdenv, meaning essentially every package has a build-time dependency on xz. For the case of

autoconf itself doesn't need xz, but in Nixpkgs xz is part of the stdenv, meaning essentially every package has a build-time dependency on xz. For the case of xz not using the upstream-generated configure would probably be doable with some effort but doing the same for glibc, gcc, gnumake etc. would be much more difficult.