Fixed for Python 3.6 / pip 9.0.1 on Mac OS X 10.13.

There was some Mac-specific code in pip that was causing issues with the `get_platform` monkey patch.

pip_custom_platform/pymonkey.py

@@ -1,3 +1,4 @@
+
 def pymonkey_argparse(argv):
     # We want to parse --platform out as early as possible so we can do patches
     # based on it
@@ -6,9 +7,15 @@ def pymonkey_argparse(argv):
     parser.add_argument('--platform')
     return parser.parse_known_args(argv)
 
-
 def pymonkey_patch(mod, args):
-    if mod.__name__ == 'distutils.util':
+    if mod.__name__ == 'distutils.sysconfig':
+        from pip_custom_platform.default_platform import get_platform_func
+        import sysconfig
+        sysconfig.get_platform = get_platform_func(args, sysconfig.get_platform)
+    elif mod.__name__ == 'distutils.util':
+        from pip_custom_platform.default_platform import get_platform_func
+        mod.get_platform = get_platform_func(args, mod.get_platform)
+    elif mod.__name__ == 'pip.pep425tags':
         from pip_custom_platform.default_platform import get_platform_func
         mod.get_platform = get_platform_func(args, mod.get_platform)
     elif mod.__name__ in ('pip', 'pip._internal') and hasattr(mod, 'main'):