Add missing target referenced by packages

Change-Id: Ie05cba843abe869764d01482b77b88530b5a154b
diff --git a/layers/BUILD.gn b/layers/BUILD.gn
index a956d34..7c55d8c 100644
--- a/layers/BUILD.gn
+++ b/layers/BUILD.gn
@@ -29,6 +29,7 @@
     ":VkLayer_parameter_validation",
     ":VkLayer_swapchain",
     ":VkLayer_threading",
+    ":VkLayer_unique_objects",
   ]
 }