stdenvs: Distinguish between extraBuildInputs and extraNativeBuildInputs

This version continues to use bash + stdenv/setup for the default
inputs.

pkgs/stdenv/generic/builder.sh

@@ -9,6 +9,7 @@ mkdir $out
 echo "export SHELL=$shell" > $out/setup
 echo "initialPath=\"$initialPath\"" >> $out/setup
 echo "defaultNativeBuildInputs=\"$defaultNativeBuildInputs\"" >> $out/setup
+echo "defaultBuildInputs=\"$defaultBuildInputs\"" >> $out/setup
 echo "$preHook" >> $out/setup
 cat "$setup" >> $out/setup