Ports and ERROR_ON_WASM_CHANGES_AFTER_LINK

I was following the advice given [here](https://github.com/emscripten-core/emscripten/issues/17019#issuecomment-1135253502) to speed up debug builds. It seems all ports are build with `-O2` optimization level, and I don't see an obvious way to configure a lower level. If there isn't a way, could it be reasonable to modify `ports.build_port` and usages of `ports.run_commands` to defer to user-defined optimization levels and fallback to `-O2` if not specified?