make certificate list change message more useful

It's a bug in our Makefile rules, make it show what the changing
certificate list was, and make it a warning so that people actually see
it.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/Makefile

@@ -137,7 +137,7 @@ endif
 
 ifneq ($(wildcard $(obj)/.x509.list),)
 ifneq ($(shell cat $(obj)/.x509.list),$(X509_CERTIFICATES))
-$(info X.509 certificate list changed)
+$(warning X.509 certificate list changed to "$(X509_CERTIFICATES)" from "$(shell cat $(obj)/.x509.list)")
 $(shell rm $(obj)/.x509.list)
 endif
 endif