Handle unpacked dimensions for struct and union members

Unpacked dimensions for struct or union members are currently silently
discarded. E.g.

```
struct packed { int x[2]; } s;
```

will elaborate successfully as a struct with a non-array int typed field.

This should instead elaborate to an unpacked array of ints typed field. And
subsequently, since unpacked arrays are not allowed in a packed struct or
union, result in an error instead.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

elab_type.cc

@@ -215,7 +215,8 @@ ivl_type_t struct_type_t::elaborate_type_raw(Design*des, NetScope*scope) const
 
 		  netstruct_t::member_t memb;
 		  memb.name = namep->name;
-		  memb.net_type = mem_vec;
+		  memb.net_type = elaborate_array_type(des, scope, *this,
+						       mem_vec, namep->index);
 		  res->append_member(des, memb);
 	    }
       }