title: What to do about warning: `extern` block uses type `u128`, which is not FFI-safe
body: <p>I used the bindgen crate to create bindings from Rust to a C library but I get a whole bunch of warnings saying:</p>
  <pre><code>warning: `extern` block uses type `u128`, which is not FFI-safe
  = note: 128-bit integers don't currently have a known stable ABI
  </code></pre>
  <p>What can I do about this warning? I assume I need to take some action to fix this, or can I ignore it?</p>