[cpp] Some missing AssignOperators

gencpp.ml

@@ -2437,6 +2437,9 @@ let gen_cpp_ast_expression_tree ctx tree =
       | OpMult -> "*="
       | OpDiv -> "/="
       | OpSub -> "-="
+      | OpAnd -> "&="
+      | OpOr -> "|="
+      | OpXor -> "^="
       | OpAssign -> "="
       | OpShl -> "<<="
       | OpShr -> ">>="