patch 8.1.1490: when a single test fails the exit code is not set

Problem:    When a single test fails the exit code is not set. (Daniel Hahler)
Solution:   Add an exit command. (closes #4506)
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index f28c941..bf64a03 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -74,10 +74,10 @@
 $(NEW_TESTS):
 	rm -f $@.res test.log messages
 	$(MAKE) -f Makefile $@.res
-	@if test -f test.log; then \
-		cat test.log; \
-	fi
 	cat messages
+	@if test -f test.log; then \
+		exit 1; \
+	fi
 
 RM_ON_RUN = test.out X* viminfo
 RM_ON_START = tiny.vim small.vim mbyte.vim mzscheme.vim test.ok benchmark.out