Merge branch vcunat@NixOS:p/stdenv (close #1840)

This branch contains a collection of stdenv-changing updates.
There's glibc 2.18 -> .19 bump and many non-intrusive PRs.

The grsecurity branch #1187 got removed at Eelco's request,
see https://github.com/NixOS/nixpkgs/issues/1840#issuecomment-39327023