make-bootstrap-tools{,-cross}.nix: Fix build after binutils changes

Broken after commit 17a344a ("binutils: Add lib output").

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

···
         for i in as ld ar ranlib nm strip readelf objdump; do
           cp ${binutils.out}/bin/$i $out/bin
         done
-        cp -d ${binutils.out}/lib/lib*.so* $out/lib
+        cp -d ${binutils.lib}/lib/lib*.so* $out/lib
 
         chmod -R u+w $out
 

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

···
         for i in as ld ar ranlib nm strip readelf objdump; do
           cp ${binutils.out}/bin/$i $out/bin
         done
-        cp -d ${binutils.out}/lib/lib*.so* $out/lib
+        cp -d ${binutils.lib}/lib/lib*.so* $out/lib
 
         chmod -R u+w $out