Make constant of enum type properly aligned

Previously, function middle::trans::trans_const result for value

```
Aaa
```

for enum like

```
enum Eee {
    Aaa,
    Bbb(u64)
}
```

was unaligned:

```
{ i8 0, [7 x i8] undef }
```

With patch applied, aligner is added to the result:

```
{ i8 0, [7 x i8] undef, [0 x i32] {} }
```

This fixes issue #13186.