xcbuild: add ProductBuildVersion

pkgs/development/tools/xcbuild/sdks.nix

···
 { runCommand, lib, toolchainName, sdkName
-, writeText, version, xcodePlatform }:
+, writeText, xcodePlatform, sdkVer, productBuildVer }:
 
 let
   inherit (lib.generators) toPlist toJSON;
···
     CanonicalName = sdkName;
     DisplayName = sdkName;
     Toolchains = [ toolchainName ];
-    Version = version;
-    MaximumDeploymentTarget = version;
+    Version = sdkVer;
+    MaximumDeploymentTarget = sdkVer;
     isBaseSDK = "YES";
   };
 
-  SystemVersion = {
+  SystemVersion = lib.optionalAttrs (productBuildVer != null) {
+    ProductBuildVersion = productBuildVer;
+  } // {
     ProductName = "Mac OS X";
-    ProductVersion = version;
+    ProductVersion = sdkVer;
   };
 in
 

pkgs/development/tools/xcbuild/wrapper.nix

···
 , CoreServices, ImageIO, CoreGraphics
 , xcodePlatform ? stdenv.targetPlatform.xcodePlatform or "MacOSX"
 , xcodeVer ? stdenv.targetPlatform.xcodeVer or "9.4.1"
-, sdkVer ? stdenv.targetPlatform.darwinSdkVersion or "10.12" }:
+, sdkVer ? stdenv.targetPlatform.darwinSdkVersion or "10.12"
+, productBuildVer ? null
+}:
 
 let
 
···
   };
 
   sdks = callPackage ./sdks.nix {
-    inherit toolchainName sdkName xcodePlatform;
-    version = sdkVer;
+    inherit toolchainName sdkName xcodePlatform sdkVer productBuildVer;
   };
 
   platforms = callPackage ./platforms.nix {