stdenv: Statically include the default build inputs

Otherwise, stdenv won't have a reference to e.g. patchelf on Linux
(because it was passed in by mkDerivation). This causes the installer
tests to fail, because having "stdenv" in the installation CD closure
is not enough to pull in all stdenv packages.

http://hydra.nixos.org/build/16546643

pkgs/stdenv/generic/builder.sh

@@ -8,6 +8,7 @@ mkdir $out
 
 echo "export SHELL=$shell" > $out/setup
 echo "initialPath=\"$initialPath\"" >> $out/setup
+echo "defaultNativeBuildInputs=\"$defaultNativeBuildInputs\"" >> $out/setup
 echo "$preHook" >> $out/setup
 cat "$setup" >> $out/setup