Issue #25764: Merge OS X test skipping from 3.5

Lib/test/test_subprocess.py

@@ -1512,6 +1512,8 @@ class POSIXProcessTestCase(BaseTestCase):
             if not enabled:
                 gc.disable()
 
+    @unittest.skipIf(
+        sys.platform == 'darwin', 'setrlimit() seems to fail on OS X')
     def test_preexec_fork_failure(self):
         # The internal code did not preserve the previous exception when
         # re-enabling garbage collection