stdenvs: Distinguish between extraBuildInputs and extraNativeBuildInputs

Additionally, instead of pulling them from `setup.sh`, route them via
Nix. This gets us one step closer to making stdenv be a plain attribute
set instead of a derivation.

pkgs/stdenv/generic/builder.sh

@@ -6,15 +6,20 @@ done
 
 mkdir $out
 
+# Buid the setup script
 echo "export SHELL=$shell" > $out/setup
 echo "initialPath=\"$initialPath\"" >> $out/setup
-echo "defaultNativeBuildInputs=\"$defaultNativeBuildInputs\"" >> $out/setup
 echo "$preHook" >> $out/setup
 cat "$setup" >> $out/setup
 
 # Allow the user to install stdenv using nix-env and get the packages
 # in stdenv.
-mkdir $out/nix-support
+mkdir -p "$out/nix-support"
+echo '# Hack to induce runtime dependencies on the default inputs' \
+    > "$out/nix-support/default-inputs.txt"
+printf '%s\n' $defaultNativeBuildInputs $defaultBuildInputs \
+    >> "$out/nix-support/default-inputs.txt"
 if [ "$propagatedUserEnvPkgs" ]; then
-    printf '%s ' $propagatedUserEnvPkgs > $out/nix-support/propagated-user-env-packages
+    printf '%s ' $propagatedUserEnvPkgs \
+        > "$out/nix-support/propagated-user-env-packages"
 fi