Fix inspect.signature tests for builtins when docstrings are compiled out.
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 6f75b77..22c8eb0 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -9,6 +9,7 @@
 import time
 import unittest
 from test import support
+from test.support import MISSING_C_DOCSTRINGS
 try:
     import _posixsubprocess
 except ImportError:
@@ -109,6 +110,8 @@
         self.assertRaises(TypeError, _posixsubprocess.fork_exec,
                           Z(),[b'1'],3,[1, 2],5,6,7,8,9,10,11,12,13,14,15,16,17)
 
+    @unittest.skipIf(MISSING_C_DOCSTRINGS,
+                     "Signature information for builtins requires docstrings")
     def test_docstring_signature_parsing(self):
 
         self.assertEqual(_testcapi.no_docstring.__doc__, None)