Solution adapted from:
https://groups.google.com/forum/#!topic/py-leveldb/VpVtc9hJatw

diff -Nurp leveldb-0.194.orig/leveldb_ext.h leveldb-0.194/leveldb_ext.h
--- leveldb-0.194.orig/leveldb_ext.h	2016-09-16 19:05:03.000000000 -0500
+++ leveldb-0.194/leveldb_ext.h	2018-10-24 17:38:06.381639156 -0500
@@ -4,9 +4,11 @@
 #ifndef __LEVELDB__MODULE__H__
 #define __LEVELDB__MODULE__H__
 
-extern "C" {
+extern "C++" {
 #include <Python.h>
+}
 
+extern "C" {
 #include "structmember.h"
 
 #include <stdlib.h>