message: Fixes case with empty module, handle case with no signatures
diff: @@ -304,8 +304,15 @@ impl ModuleCodeGenerator<CraneliftFunctionCodeGenerator, Caller, CodegenError>
  let trampolines = Arc::new(Trampolines::new(&*self.isa, module_info));
  + let signatures_empty = Map::new();
  + let signatures = if self.signatures.is_some() {
  + &self.signatures.as_ref().unwrap()
  + } else {
  + &signatures_empty
  + };
  +
  let (func_resolver, backend_cache) = func_resolver_builder.finalize(
  - &self.signatures.as_ref().unwrap(),
  + signatures,
  Arc::clone(&trampolines),
  handler_data.clone(),
  )?;
  