Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Includes/cpython/getargs.pxd

Index: third_party/cython/src/Cython/Includes/cpython/getargs.pxd
diff --git a/third_party/cython/src/Cython/Includes/cpython/getargs.pxd b/third_party/cython/src/Cython/Includes/cpython/getargs.pxd
new file mode 100644
index 0000000000000000000000000000000000000000..591aefbfdeda65dc902c679d6d3a19a1c0c1f0ed
--- /dev/null
+++ b/third_party/cython/src/Cython/Includes/cpython/getargs.pxd
@@ -0,0 +1,13 @@
+from cpython.ref cimport PyObject
+
+cdef extern from "Python.h":
+    #####################################################################
+    # 5.5 Parsing arguments and building values
+    #####################################################################
+    ctypedef struct va_list
+    int PyArg_ParseTuple(object args, char *format, ...) except 0
+    int PyArg_VaParse(object args, char *format, va_list vargs) except 0
+    int PyArg_ParseTupleAndKeywords(object args, object kw, char *format, char *keywords[], ...) except 0
+    int PyArg_VaParseTupleAndKeywords(object args, object kw, char *format, char *keywords[], va_list vargs) except 0
+    int PyArg_Parse(object args, char *format, ...) except 0
+    int PyArg_UnpackTuple(object args, char *name, Py_ssize_t min, Py_ssize_t max, ...) except 0