bpo-30207: Rename test.test_support to test.support. (#1353)

To simplify backports from Python 3, the test.test_support module
was converted into a package and renamed to test.support.  The
test.script_helper module was moved into the test.support package.
Names test.test_support and test.script_helper are left as aliases to
test.support and test.support.script_helper.
diff --git a/Lib/test/test_compiler.py b/Lib/test/test_compiler.py
index 4598811..c98e494 100644
--- a/Lib/test/test_compiler.py
+++ b/Lib/test/test_compiler.py
@@ -26,7 +26,7 @@
         # warning: if 'os' or 'test_support' are moved in some other dir,
         # they should be changed here.
         libdir = os.path.dirname(os.__file__)
-        testdir = os.path.dirname(test.test_support.__file__)
+        testdir = test.test_support.TEST_HOME_DIR
 
         for dir in [testdir]:
             for basename in "test_os.py",: