message: Use entry API instead of a match
  This makes the code easier to read and also avoids looking up the
  position in the map twice. The clone of `unit` is very cheap since it is
  an Rc.
diff: @@ -475,13 +475,11 @@ pub fn create_bcx<'a, 'cfg>(
  extra_args = Some(args);
  }
  - if let Some(mut args) = extra_args {
  - match extra_compiler_args.get_mut(&unit) {
  - None => {
  - extra_compiler_args.insert(unit.clone(), args);
  - }
  - Some(existing) => existing.append(&mut args),
  - }
  + if let Some(args) = extra_args {
  + extra_compiler_args
  + .entry(unit.clone())
  + .or_default()
  + .extend(args);
  }
  }
  }
  