Fixes sandboxed build of glibc. Discussion about a similar failure on aarch64 at:8bfa9f528c. Picked from the following cross-trunk evaluation: http://hydra.nixos.org/eval/1349278 based on nixpkgs commit1f32d4b4eb. armv5tel job: http://hydra.nixos.org/build/51569718 armv6l job: http://hydra.nixos.org/build/51569717 armv7l job: http://hydra.nixos.org/build/51569713