Issues #22980, 23969: For OS X, use PEP 3149-style file names for extension

module binaries, with a platform triple of just "darwin", resulting in
file names like:

    _ssl.cpython-35m-darwin.so

rather than just _ssl.so as previously.

Instead of attempting to encode differences in CPU architecture and OS X
deployment targets in the file name as is done on other platforms,
these continue to be managed by the use of Apple multi-architecture
("fat") files, by the system dynamic loader, and by logic in higher-levels
like sysconfig.get_platform() and pip.

Lib/test/test_sysconfig.py

@@ -404,6 +404,10 @@ class TestSysConfig(unittest.TestCase):
             else: # 8 byte pointer size
                 self.assertTrue(suffix.endswith('x86_64-linux-gnu.so'), suffix)
 
+    @unittest.skipUnless(sys.platform == 'darwin', 'OS X-specific test')
+    def test_osx_ext_suffix(self):
+        suffix = sysconfig.get_config_var('EXT_SUFFIX')
+        self.assertTrue(suffix.endswith('-darwin.so'), suffix)
 
 class MakefileTests(unittest.TestCase):