scripts: Make safe_structs call pnext handlers

Safe structs will now make deep copies of the attendant pnext chain.

Change-Id: I34d6dfed9ce8222c197b83448ad7ee420b55df8c
diff --git a/layers/generated/vk_safe_struct.h b/layers/generated/vk_safe_struct.h
index bbf6711..236098c 100644
--- a/layers/generated/vk_safe_struct.h
+++ b/layers/generated/vk_safe_struct.h
@@ -34,6 +34,7 @@
 #include <vulkan/vulkan.h>
 
 void *SafePnextCopy(const void *pNext);
+void FreePnextChain(const void *head);
 void FreePnextChain(void *head);