makeWrapper: fix regression introduced in #24944

In some cases wrappers could not be made. See e.g.
https://github.com/NixOS/nixpkgs/pull/24944#issuecomment-321175692

pkgs/build-support/setup-hooks/make-wrapper.sh

@@ -33,7 +33,7 @@ makeWrapper() {
     local params varName value command separator n fileNames
     local argv0 flagsBefore flags
 
-    assertExecutable "${file}"
+    assertExecutable "${original}"
 
     mkdir -p "$(dirname "$wrapper")"