This may be a slightly "bogus" location to provide for ESSA variables,
but it can be useful for debugging. For instance, where previously you
might just see
```
SSA variable x | ...
SSA variable x | ...
SSA variable x | ...
SSA variable x | ...
SSA variable x | ...
SSA variable x | ...
```
where each instance of `SSA variable x` was just a bare string, now
each occurrence will tell you (via its location) _where_ this variable
is being (re)defined.