xcbuild: include version in sdk

Without this xcbuild can detect an incorrect version for store paths
that have a sequence of digits in their hash.

ld: malformed 32-bit x.y.z version number: 85294

/nix/store/yz966rdvw1blblvzs15pxpcd85294isw-MacOSX.platform/Developer/SDKs/MacOSX.sdk

pkgs/development/tools/xcbuild/sdk.nix

···
 { stdenv, writeText, toolchainName, sdkName, xcbuild }:
 
 let
+  # TODO: expose MACOSX_DEPLOYMENT_TARGET in nix so we can use it here.
+  version = "10.10";
 
   SDKSettings = {
     CanonicalName = sdkName;
     DisplayName = sdkName;
     Toolchains = [ toolchainName ];
-    Version = "10.10";
-    MaximumDeploymentTarget = "10.10";
+    Version = version;
+    MaximumDeploymentTarget = version;
     isBaseSDK = "YES";
   };
 
   SystemVersion = {
     ProductName = "Mac OS X";
-    ProductVersion = "10.10";
+    ProductVersion = version;
   };
-
 in
 
 stdenv.mkDerivation {
-  name = "MacOSX.sdk";
+  name = "MacOSX${version}.sdk";
+  inherit version;
+
   buildInputs = [ xcbuild ];
+
   buildCommand = ''
     mkdir -p $out/
     plutil -convert xml1 -o $out/SDKSettings.plist ${writeText "SDKSettings.json" (builtins.toJSON SDKSettings)}