message: Document why Send and Sync are safe.
diff: @@ -72,10 +72,12 @@ impl std::ops::Deref for FunctionBodyPtr {
  }
  /// # Safety
  -/// TODO:
  +/// The VMFunctionBody that this points to is opaque, so there's no data to
  +/// read or write through this pointer. This is essentially a usize.
  unsafe impl Send for FunctionBodyPtr {}
  /// # Safety
  -/// TODO:
  +/// The VMFunctionBody that this points to is opaque, so there's no data to
  +/// read or write through this pointer. This is essentially a usize.
  unsafe impl Sync for FunctionBodyPtr {}
  /// Pointers to section data.
  