stockfish: update version 6 to 7

pkgs/games/stockfish/default.nix

@@ -1,32 +1,36 @@
 { stdenv, fetchurl, unzip }:
+
+let arch = if stdenv.isx86_64 then "x86-64" else
+           if stdenv.isi686 then "x86-32" else
+           "unknown";
+in
+
 stdenv.mkDerivation rec {
-  version = "6";
-  name = "stockfish-${version}";
+
+  name = "stockfish-7";
+
   src = fetchurl {
-    url = https://stockfish.s3.amazonaws.com/stockfish-6-src.zip;
-    sha256 = "a69a371d3f84338cefde4575669bd930d186b046a10fa5ab0f8d1aed6cb204c3";
+    url = "https://stockfish.s3.amazonaws.com/${name}-src.zip";
+    sha256 = "0djzg3h5d9qs27snf0rr6zl6iaki1jb84v8m8k3c2lcjbj2vpwc9";
   };
-  buildPhase = ''
-  cd src
-  make build ARCH=x86-64
-  '';
-  buildInputs = [
-        stdenv
-        unzip
-  ];
+
+  buildInputs = [ unzip ];
+  postUnpack = "sourceRoot+=/src";
+  makeFlags = [ "PREFIX=$out" "ARCH=${arch}" ];
+  buildFlags = "build";
+
   enableParallelBuilding = true;
-  installPhase = ''
-  mkdir -p $out/bin
-  cp -pr stockfish $out/bin
-  '';
+
   meta = with stdenv.lib; {
-    homepage = https://stockfishchess.org/;
+    homepage = "https://stockfishchess.org/";
     description = "Strong open source chess engine";
     longDescription = ''
       Stockfish is one of the strongest chess engines in the world. It is also
       much stronger than the best human chess grandmasters.
       '';
-    maintainers = with maintainers; [ luispedro ];
+    maintainers = with maintainers; [ luispedro peti ];
+    platforms = with platforms; i686 ++ x86_64;
     license = licenses.gpl2;
   };
+
 }