test/Makefile: proper return code for "make check"

test/Makefile

@@ -2,13 +2,14 @@
 
 check:
 	@[ "$$EUID" == "0" ] || { echo "'check' must be run as root! Please use 'sudo'."; exit 1; }
-	@for i in TEST-[0-9]*; do \
+	@{ ret=0; \
+	for i in TEST-[0-9]*; do \
 		[ -d $$i ] || continue ; \
 		[ -f $$i/Makefile ] || continue ; \
 		if [ -n "$$TESTS" ]; then t=$${i##TEST-}; t=$${t%%-*}; [ "$${TESTS#*$$t*}" != "$$TESTS" ] || continue; fi; \
 		if [ -n "$$SKIP" ]; then t=$${i##TEST-}; t=$${t%%-*}; [ "$${SKIP#*$$t*}" != "$$SKIP" ] && continue; fi; \
-		$(MAKE) -C $$i all ; \
-	done
+		$(MAKE) -C $$i all ; ret=$$((ret + $$?)); \
+	done; exit $$ret; }
 
 clean:
 	@for i in TEST-[0-9]*; do \