Fail the build when using a user tag on a non-legacy module.

The supported mechanism is to explicitly add the module
name to the PRODUCT_PACKAGES of the relevant product definitions.

Change-Id: Ic754446e15965d468d1bbe85864275e2cda9b3aa
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 04270f0..6f4b826 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -71,7 +71,9 @@
 
 ifneq ($(filter $(LOCAL_MODULE_TAGS),user),)
   ifeq ($(filter $(GRANDFATHERED_USER_MODULES),$(LOCAL_MODULE)),)
-    $(warning using user tag on $(LOCAL_MODULE) at $(LOCAL_PATH))
+    $(warning *** Module name: $(LOCAL_MODULE))
+    $(warning *** Makefile location: $(LOCAL_PATH))
+    $(error user tag detected on new module - user tags are only supported on legacy modules)
   endif
 endif