binutils: try to move headers around only when --host/--target differ (#215989)

Without the change `pkgsMusl.pkgsStatic.buildPackages.binutils.bintools`
build fails as:

    $ ln: failed to create symbolic link './include': File exists

This happens because both host and target are `x86_64-unknown-linux-musl`.
But `hostPlatform` differs from `targetPlatform` by `isStatic` value.

By `./configure`'s standard it's not yet a cross-compilation. The change
tries to move things around only when tuples change.

pkgs/development/tools/misc/binutils/default.nix

@@ -234,7 +234,7 @@ stdenv.mkDerivation (finalAttrs: {
   #   $out/$host/$target/include/* to $dev/include/*
   # TODO(trofi): fix installation paths upstream so we could remove this
   # code and have "lib" output unconditionally.
-  postInstall = lib.optionalString (hostPlatform != targetPlatform) ''
+  postInstall = lib.optionalString (hostPlatform.config != targetPlatform.config) ''
     ln -s $out/${hostPlatform.config}/${targetPlatform.config}/lib/*     $out/lib/
     ln -s $out/${hostPlatform.config}/${targetPlatform.config}/include/* $dev/include/
   '';