protobuf3: clean up cross compile

pkgs/development/libraries/protobuf/3.1.nix

@@ -1,7 +1,6 @@
-{ callPackage, useExternalProtoc, buildProtobuf, ... }:
+{ callPackage, ... }:
 
 callPackage ./generic-v3.nix {
   version = "3.1.0";
   sha256 = "0qlvpsmqgh9nw0k4zrxlxf75pafi3p0ahz99v6761b903y8qyv4i";
-  inherit useExternalProtoc buildProtobuf;
 }

pkgs/development/libraries/protobuf/3.4.nix

@@ -1,7 +1,6 @@
-{ callPackage, lib, useExternalProtoc, buildProtobuf, ... }:
+{ callPackage, lib, ... }:
 
 lib.overrideDerivation (callPackage ./generic-v3.nix {
   version = "3.4.1";
   sha256 = "1lzxmbqlnmi34kymnf399azv86gmdbrf71xiad6wc24bzpkzqybb";
-  inherit useExternalProtoc buildProtobuf;
 }) (attrs: { NIX_CFLAGS_COMPILE = "-Wno-error"; })

pkgs/development/libraries/protobuf/3.5.nix

@@ -1,7 +1,6 @@
-{ callPackage, lib, useExternalProtoc, buildProtobuf, ... }:
+{ callPackage, lib, ... }:
 
 lib.overrideDerivation (callPackage ./generic-v3.nix {
   version = "3.5.1.1";
   sha256 = "1h4xydr5j2zg1888ncn8a1jvqq8fgpgckrmjg6lqzy9jpkvqvfdk";
-  inherit useExternalProtoc buildProtobuf;
 }) (attrs: { NIX_CFLAGS_COMPILE = "-Wno-error"; })

pkgs/development/libraries/protobuf/3.6.nix

@@ -1,7 +1,6 @@
-{ callPackage, useExternalProtoc, buildProtobuf, ... }:
+{ callPackage, ... }:
 
 callPackage ./generic-v3.nix {
   version = "3.6.1";
   sha256 = "1bg40miylzpy2wgbd7l7zjgmk43l12q38fq0zkn0vzy1lsj457sq";
-  inherit useExternalProtoc buildProtobuf;
 }

pkgs/development/libraries/protobuf/generic-v3.nix

@@ -1,13 +1,12 @@
 { stdenv
 , fetchFromGitHub
 , autoreconfHook, zlib, gmock, which, buildPackages
-, useExternalProtoc
-, buildProtobuf ? null
 , version, sha256
 , ...
 }:
 
-stdenv.mkDerivation rec {
+let
+mkProtobufDerivation = buildProtobuf: stdenv: stdenv.mkDerivation rec {
   name = "protobuf-${version}";
 
   # make sure you test also -A pythonPackages.protobuf
@@ -31,10 +30,10 @@ stdenv.mkDerivation rec {
   '';
 
   nativeBuildInputs = [ autoreconfHook buildPackages.which buildPackages.stdenv.cc ]
-                      ++ stdenv.lib.optional useExternalProtoc [ buildProtobuf ];
+                      ++ (if buildProtobuf == null then [] else [ buildProtobuf ]);
 
   buildInputs = [ zlib ];
-  configureFlags = stdenv.lib.optional useExternalProtoc [ "--with-protoc=${buildProtobuf}/bin/protoc" ];
+  configureFlags = if buildProtobuf == null then [] else [ "--with-protoc=${buildProtobuf}/bin/protoc" ];
 
   enableParallelBuilding = true;
 
@@ -59,4 +58,7 @@ stdenv.mkDerivation rec {
   };
 
   passthru.version = version;
-}
+};
+in mkProtobufDerivation(if (stdenv.buildPlatform != stdenv.hostPlatform)
+                        then (mkProtobufDerivation null buildPackages.stdenv)
+                        else null) stdenv

pkgs/top-level/all-packages.nix

@@ -11726,30 +11726,10 @@ with pkgs;
 
   protobuf = protobuf3_6;
 
-  protobuf3_6 = callPackage ../development/libraries/protobuf/3.6.nix {
-    useExternalProtoc = (stdenv.hostPlatform != stdenv.buildPlatform);
-    buildProtobuf = if (stdenv.hostPlatform != stdenv.buildPlatform)
-                    then buildPackages.protobuf3_6
-                    else null;
-  };
-  protobuf3_5 = callPackage ../development/libraries/protobuf/3.5.nix {
-    useExternalProtoc = (stdenv.hostPlatform != stdenv.buildPlatform);
-    buildProtobuf = if (stdenv.hostPlatform != stdenv.buildPlatform)
-                    then buildPackages.protobuf3_5
-                    else null;
-  };
-  protobuf3_4 = callPackage ../development/libraries/protobuf/3.4.nix {
-    useExternalProtoc = (stdenv.hostPlatform != stdenv.buildPlatform);
-    buildProtobuf = if (stdenv.hostPlatform != stdenv.buildPlatform)
-                    then buildPackages.protobuf3_4
-                    else null;
-  };
-  protobuf3_1 = callPackage ../development/libraries/protobuf/3.1.nix {
-    useExternalProtoc = (stdenv.hostPlatform != stdenv.buildPlatform);
-    buildProtobuf = if (stdenv.hostPlatform != stdenv.buildPlatform)
-                    then buildPackages.protobuf3_1
-                    else null;
-  };
+  protobuf3_6 = callPackage ../development/libraries/protobuf/3.6.nix { };
+  protobuf3_5 = callPackage ../development/libraries/protobuf/3.5.nix { };
+  protobuf3_4 = callPackage ../development/libraries/protobuf/3.4.nix { };
+  protobuf3_1 = callPackage ../development/libraries/protobuf/3.1.nix { };
   protobuf2_5 = callPackage ../development/libraries/protobuf/2.5.nix { };
 
   protobufc = callPackage ../development/libraries/protobufc/1.3.nix { };