Duplicate function argument names

For now, this is a valid IELE code:
```
define @func(%a, %a) {
  ret %a
}
```

Compiles and executes without a question. Returns the last argument value, of course, because of how cells work. And I couldn't find any mention of argument names to be required to be unique in the semantics.

Just wanted to clarify for history if this is by design, and if it serves some purpose?