binutils: Respect the targetPlatform

Use `buildPackages.binutils` to get build = host != target binutils,
i.e. the old `binutilsCross`, and use
`buildPackages.buildPackages.binutils` to get build = host = target
binutils, i.e. the old `binutils`.

`buildPackages` chains like this are supposed to remove the need for
all such `*Cross` derivations. We start with binutils because it's
comparatively easy.

No hashes of cross-tests should be changed

pkgs/stdenv/linux/make-bootstrap-tools-cross.nix

@@ -70,8 +70,6 @@ let
 
   pkgs = pkgsFun ({inherit system;} // selectedCrossSystem);
 
-  inherit (pkgs.buildPackages) stdenv nukeReferences cpio binutilsCross;
-
   glibc = pkgs.buildPackages.libcCross;
   bash = pkgs.bash;
   findutils = pkgs.findutils;
@@ -126,11 +124,15 @@ rec {
 
   build =
 
-    stdenv.mkDerivation {
+    pkgs.buildPackages.stdenv.mkDerivation {
       name = "stdenv-bootstrap-tools-cross";
       crossConfig = pkgs.hostPlatform.config;
 
-      buildInputs = [nukeReferences cpio binutilsCross];
+      buildInputs = [
+        pkgs.buildPackages.nukeReferences
+        pkgs.buildPackages.cpio
+        pkgs.buildPackages.binutils
+      ];
 
       buildCommand = ''
         set -x
@@ -261,7 +263,7 @@ rec {
       allowedReferences = [];
     };
 
-  dist = stdenv.mkDerivation {
+  dist = pkgs.buildPackages.stdenv.mkDerivation {
     name = "stdenv-bootstrap-tools-cross";
 
     buildCommand = ''