Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Utility/CommonTypes.c

Index: third_party/cython/src/Cython/Utility/CommonTypes.c
diff --git a/third_party/cython/src/Cython/Utility/CommonTypes.c b/third_party/cython/src/Cython/Utility/CommonTypes.c
new file mode 100644
index 0000000000000000000000000000000000000000..c2403cbf98a3d7e1bcda898ea9757ea41d7181cb
--- /dev/null
+++ b/third_party/cython/src/Cython/Utility/CommonTypes.c
@@ -0,0 +1,48 @@
+/////////////// FetchCommonType.proto ///////////////
+
+static PyTypeObject* __Pyx_FetchCommonType(PyTypeObject* type);
+
+/////////////// FetchCommonType ///////////////
+
+static PyTypeObject* __Pyx_FetchCommonType(PyTypeObject* type) {
+    PyObject* fake_module;
+    PyTypeObject* cached_type = NULL;
+
+    fake_module = PyImport_AddModule((char*) "_cython_" CYTHON_ABI);
+    if (!fake_module) return NULL;
+    Py_INCREF(fake_module);
+
+    cached_type = (PyTypeObject*) PyObject_GetAttrString(fake_module, type->tp_name);
+    if (cached_type) {
+        if (!PyType_Check((PyObject*)cached_type)) {
+            PyErr_Format(PyExc_TypeError,
+                "Shared Cython type %.200s is not a type object",
+                type->tp_name);
+            goto bad;
+        }
+        if (cached_type->tp_basicsize != type->tp_basicsize) {
+            PyErr_Format(PyExc_TypeError,
+                "Shared Cython type %.200s has the wrong size, try recompiling",
+                type->tp_name);
+            goto bad;
+        }
+    } else {
+        if (!PyErr_ExceptionMatches(PyExc_AttributeError)) goto bad;
+        PyErr_Clear();
+        if (PyType_Ready(type) < 0) goto bad;
+        if (PyObject_SetAttrString(fake_module, type->tp_name, (PyObject*) type) < 0)
+            goto bad;
+        Py_INCREF(type);
+        cached_type = type;
+    }
+
+done:
+    Py_DECREF(fake_module);
+    // NOTE: always returns owned reference, or NULL on error
+    return cached_type;
+
+bad:
+    Py_XDECREF(cached_type);
+    cached_type = NULL;
+    goto done;
+}