Warn when new modules are found that use user tags

Change-Id: I49369cc1596f269e0964f0a6a88bcc7152209bde
diff --git a/core/definitions.mk b/core/definitions.mk
index 74c9565..7c69ce1 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1848,6 +1848,9 @@
 # when requested.
 include $(BUILD_SYSTEM)/distdir.mk
 
+# -----------------------------------------------------------------
+# The modules allowed to use a user tag
+include $(BUILD_SYSTEM)/user_tags.mk
 
 # broken:
 #	$(foreach file,$^,$(if $(findstring,.a,$(suffix $file)),-l$(file),$(file)))