patch 8.1.0413: test output is duplicated or missing

Problem:    Test output is duplicated or missing.
Solution:   Adjust the MS-Windows and Unix test makefiles. (Ken Takata,
            closes #3452)
diff --git a/src/testdir/Make_dos.mak b/src/testdir/Make_dos.mak
index 6a86d3e..ebd8dd1 100644
--- a/src/testdir/Make_dos.mak
+++ b/src/testdir/Make_dos.mak
@@ -112,7 +112,10 @@
 # to write and a lot easier to read and debug.
 # Limitation: Only works with the +eval feature.
 
-newtests: $(NEW_TESTS)
+newtests: newtestssilent
+	@if exist messages (findstr "SKIPPED FAILED" messages > nul) && type messages
+
+newtestssilent: $(NEW_TESTS)
 
 .vim.res:
 	@echo $(VIMPROG) > vimcmd