message: Address map cloning comment
diff: @@ -319,9 +319,9 @@ fn gen_binary(
  }
  /// An environment for translating Bril into CLIF.
  -struct CompileEnv {
  +struct CompileEnv<'a> {
  vars: HashMap<String, Variable>,
  - var_types: HashMap<String, bril::Type>,
  + var_types: HashMap<&'a String, &'a bril::Type>,
  rt_refs: EnumMap<RTFunc, ir::FuncRef>,
  blocks: HashMap<String, ir::Block>,
  func_refs: HashMap<String, ir::FuncRef>,
  @@ -566,11 +566,6 @@ impl<M: Module> Translator<M> {
  })
  .collect();
  - // Cloning this map is not so great, but I am pretty bad at Rust!
  - let var_types = var_types
  - .into_iter()
  - .map(|(k, v)| (k.clone(), v.clone()))
  - .collect();
  let env = CompileEnv {
  vars,
  var_types,
  