Merge 'staging' into closure-size

This is mainly to get the update of bootstrap tools.
Otherwise there were mysterious segfaults:
https://github.com/NixOS/nixpkgs/pull/7701#issuecomment-203389817

pkgs/development/compilers/gcc/5/default.nix

@@ -500,8 +500,6 @@ stdenv.mkDerivation ({
 
   inherit (stdenv) is64bit;
 
-  setupHook = ./use-old-abi.sh;
-
   meta = {
     homepage = http://gcc.gnu.org/;
     license = stdenv.lib.licenses.gpl3Plus;  # runtime support libraries are typically LGPLv3+

pkgs/development/compilers/gcc/5/use-old-abi.sh

@@ -1 +0,0 @@
-NIX_CFLAGS_COMPILE+=" -D_GLIBCXX_USE_CXX11_ABI=0"