pond: Simplify platform logic

pkgs/applications/networking/instant-messengers/pond/default.nix

@@ -2,7 +2,6 @@
   fetchgit, fetchhg, fetchbzr, fetchsvn }:
 
 let
-  isx86_64 = stdenv.lib.any (n: n == stdenv.system) stdenv.lib.platforms.x86_64;
   gui = true; # Might be implemented with nixpkgs config.
 in
 buildGoPackage rec {
@@ -22,11 +21,11 @@ buildGoPackage rec {
 
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [ trousers gtk3 gtkspell3 ]
-    ++ stdenv.lib.optional isx86_64 dclxvi
+    ++ stdenv.lib.optional stdenv.hostPlatform.isx86_64 dclxvi
     ++ stdenv.lib.optionals gui [ wrapGAppsHook ];
   buildFlags = stdenv.lib.optionalString (!gui) "-tags nogui";
   excludedPackages = "\\(appengine\\|bn256cgo\\)";
-  postPatch = stdenv.lib.optionalString isx86_64 ''
+  postPatch = stdenv.lib.optionalString stdenv.hostPlatform.isx86_64 ''
     grep -r 'bn256' | awk -F: '{print $1}' | xargs sed -i \
       -e "s,golang.org/x/crypto/bn256,github.com/agl/pond/bn256cgo,g" \
       -e "s,bn256\.,bn256cgo.,g"