Xcode: Enable BuildIndependentTargetsInParallel

This fixes a warning when running xcodebuild directly

extras/Projucer/Source/ProjectSaving/jucer_ProjectExport_Xcode.h

@@ -3498,6 +3498,7 @@ private:
         std::map<String, String> attributes;
 
         attributes["LastUpgradeCheck"] = "1340";
+        attributes["BuildIndependentTargetsInParallel"] = "YES";
         attributes["ORGANIZATIONNAME"] = getProject().getCompanyNameString().quoted();
 
         if (projectType.isGUIApplication() || projectType.isAudioPlugin())