patch 8.1.2259: running tests may leave XfakeHOME behind

Problem:    Running tests may leave XfakeHOME behind.
Solution:   Source summarize.vim without using setup.vim. (closes #5177)
            Also fix that on MS-Windows the test log isn't echoed.
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index d4290f9..a0520e0 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -54,7 +54,7 @@
 		then cp test.log test_result.log; \
 		else echo No failures reported > test_result.log; \
 		fi"
-	$(RUN_VIMTEST) $(NO_INITS) -S summarize.vim messages $(REDIR_TEST_TO_NULL)
+	$(VIMPROG) -u NONE $(NO_INITS) -S summarize.vim messages $(REDIR_TEST_TO_NULL)
 	@echo
 	@echo 'Test results:'
 	@cat test_result.log