testsuite/Makefile.in: ensure .test-rules.make is regenerated

That is, regenerate when Makefile.in is modified.
Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>

testsuite/Makefile.in

@@ -96,7 +96,9 @@ dlopen-test$(EXEEXT): dlopen-test.$(OBJEXT) testutils.$(OBJEXT)
 	$(LINK) dlopen-test.$(OBJEXT) -ldl -o dlopen-test$(EXEEXT)
 
 .PHONY: test-rules
-test-rules:
+test-rules: .test-rules.make
+
+.test-rules.make: Makefile.in
 	(for f in $(TS_NETTLE) $(TS_HOGWEED) $(EXTRA_TARGETS) ; do \
 	  echo $$f'$$(EXEEXT): '$$f'.$$(OBJEXT)' ; \
 	  echo '	$$(LINK) '$$f'.$$(OBJEXT) $$(TEST_OBJS) -o '$$f'$$(EXEEXT)' ; \
@@ -107,6 +109,10 @@ test-rules:
 	  echo '	$$(LINK_CXX) '$$f'.$$(OBJEXT) $$(TEST_OBJS) -o '$$f'$$(EXEEXT)' ; \
 	  echo ; \
 	done) > $(srcdir)/.test-rules.make
+	@echo "******************************************************************"
+	@echo "testsuite Makefile rules have been regenerated; please re-run make"
+	@echo "******************************************************************"
+	false
 
 include $(srcdir)/.test-rules.make