Hopefully fixes sandboxed build of glibc on aarch64, as discussed on8bfa9f528c. Picked from the following cross-trunk evaluation: http://hydra.nixos.org/eval/1341395 based on nixpkgs commitbb3ef8a95c. build job: http://hydra.nixos.org/build/50125932 (busybox's hash not changing is not a bug!)