[cpp] Reduce debug level

gencpp.ml

@@ -229,7 +229,7 @@ let new_context common_ctx writer debug file_info =
    ctx_cppast = Common.defined_value_safe common_ctx Define.CppAst <>"";
    ctx_calling = false;
    ctx_assigning = false;
-   ctx_debug_level = 2;
+   ctx_debug_level = debug;
    ctx_dump_src_pos = (fun() -> ());
    ctx_return_from_block = false;
    ctx_tcall_expand_args = false;