This patch has been merged upstream. Drop next update.
Commit: 39ca75bac294a69504e1ea551e1615816e3aec06

Index: src/CXX/Python3/cxxsupport.cxx
--- src/CXX/Python3/cxxsupport.cxx.orig
+++ src/CXX/Python3/cxxsupport.cxx
@@ -48,7 +48,7 @@ Py_ssize_t numeric_limits_max()
 #if !defined(Py_LIMITED_API)
 Py_UNICODE unicode_null_string[1] = { 0 };
 #endif
-Py_UCS4 ucs4_null_string[1] = { 0 };
+char32_t ucs4_null_string[1] = { 0 };
 
 Type Object::type() const
 {
