bpo-40275: Use new test.support helper submodules in tests (GH-21151)

Use new test.support helper submodules in tests:

* distutils tests
* test_buffer
* test_compile
* test_filecmp
* test_fileinput
* test_readline
* test_smtpnet
* test_structmembers
* test_tools
diff --git a/Lib/test/test_structmembers.py b/Lib/test/test_structmembers.py
index 57ec45f..07d2f62 100644
--- a/Lib/test/test_structmembers.py
+++ b/Lib/test/test_structmembers.py
@@ -1,8 +1,9 @@
 import unittest
-from test import support
+from test.support import import_helper
+from test.support import warnings_helper
 
 # Skip this test if the _testcapi module isn't available.
-support.import_module('_testcapi')
+import_helper.import_module('_testcapi')
 from _testcapi import _test_structmembersType, \
     CHAR_MAX, CHAR_MIN, UCHAR_MAX, \
     SHRT_MAX, SHRT_MIN, USHRT_MAX, \
@@ -116,27 +117,27 @@
 class TestWarnings(unittest.TestCase):
 
     def test_byte_max(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_BYTE = CHAR_MAX+1
 
     def test_byte_min(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_BYTE = CHAR_MIN-1
 
     def test_ubyte_max(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_UBYTE = UCHAR_MAX+1
 
     def test_short_max(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_SHORT = SHRT_MAX+1
 
     def test_short_min(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_SHORT = SHRT_MIN-1
 
     def test_ushort_max(self):
-        with support.check_warnings(('', RuntimeWarning)):
+        with warnings_helper.check_warnings(('', RuntimeWarning)):
             ts.T_USHORT = USHRT_MAX+1