[3.8] bpo-37250: put back tp_print for backwards compatibility (GH-14193)

This is a 3.8-only compatibility measure for third-party Cython-based sdists.

https://bugs.python.org/issue37250
diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index a65aaf6..5a0ac4a 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -256,6 +256,9 @@
     destructor tp_finalize;
     vectorcallfunc tp_vectorcall;
 
+    /* bpo-37250: kept for backwards compatibility in CPython 3.8 only */
+    Py_DEPRECATED(3.8) int (*tp_print)(PyObject *, FILE *, int);
+
 #ifdef COUNT_ALLOCS
     /* these must be last and never explicitly initialized */
     Py_ssize_t tp_allocs;