Set test_support.verbose to 0, to signal tests only to generate
portable output.
diff --git a/Lib/test/autotest.py b/Lib/test/autotest.py
index 6791034..94ae9c1 100644
--- a/Lib/test/autotest.py
+++ b/Lib/test/autotest.py
@@ -42,6 +42,8 @@
 import sys
 import getopt
 import traceback
+import test_support
+test_support.verbose = 0
 from test_support import *
 
 # Exception raised when the test failed (not the same as in test_support)