cross-stdenv: Only prune most overrides in the final stage

Before all overrides were also pruned in the previous stage, now
only gcc and binutils are, because they alone care about about the
target platform. The rest of the overrides don't, so it's better to
preserve them in order to avoid spurious rebuilds.

pkgs/stdenv/linux/default.nix

@@ -298,12 +298,14 @@ in
         */
 
       overrides = self: super: {
-        gcc = cc;
-
         inherit (prevStage)
-          gzip bzip2 xz bash binutils coreutils diffutils findutils gawk
+          gzip bzip2 xz bash coreutils diffutils findutils gawk
           glibc gnumake gnused gnutar gnugrep gnupatch patchelf
           attr acl paxctl zlib pcre;
+      } // lib.optionalAttrs (super.targetPlatform == localSystem) {
+        # Need to get rid of these when cross-compiling.
+        inherit (prevStage) binutils;
+        gcc = cc;
       };
     };
   })