How can I disable sign-extension opcode

Hi I'm currently working on a project which has a custom wasm loader, it does not have support for sign-extension.When I compiled my code to wasm and instantiate with its loader, it showed error message like : invalid opcode 192, which pointed to sign-extension. After some googling I found that I could add -mno-sign-ext to disable sign extension.But when I do, the generated wasm still has opcode like i32.extends_8. My question is , how do I completely disable this family of the opcodes, or at least get a warning about its location. Thank you in advance.