Add the missing importlib.test.extension.util.

Lib/importlib/test/extension/util.py

+import imp
+import os
+import sys
+
+PATH = None
+EXT = None
+FILENAME = None
+NAME = '_testcapi'
+_file_exts = [x[0] for x in imp.get_suffixes() if x[2] == imp.C_EXTENSION]
+try:
+    for PATH in sys.path:
+        for EXT in _file_exts:
+            FILENAME = NAME + EXT
+            FILEPATH = os.path.join(PATH, FILENAME)
+            if os.path.exists(os.path.join(PATH, FILENAME)):
+                raise StopIteration
+    else:
+        PATH = EXT = FILENAME = FILEPATH = None
+except StopIteration:
+    pass
+del _file_exts