always insert the module into sys.modules right after creating it in Py3 (Py2 does it for us)

Cython/Compiler/ModuleNode.py

@@ -2088,8 +2088,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 Naming.pymoduledef_cname))
         code.putln("#endif")
         code.putln(code.error_goto_if_null(env.module_cname, self.pos))
-        if env.is_package:
-            # CPython may not have put us into sys.modules yet, but relative imports require it
+        # CPython may not have put us into sys.modules yet, but relative imports and reimports require it
+        code.putln("#if PY_MAJOR_VERSION >= 3")
         code.putln("{")
         code.putln("PyObject *modules = PyImport_GetModuleDict(); %s" %
                    code.error_goto_if_null("modules", self.pos))
@@ -2098,6 +2098,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             env.module_name, env.module_cname), self.pos))
         code.putln("}")
         code.putln("}")
+        code.putln("#endif")
         code.putln(
             '%s = PyImport_AddModule(__Pyx_NAMESTR(__Pyx_BUILTIN_MODULE_NAME)); %s' % (
                 Naming.builtins_cname,