Handle discriminators

When comparing the output of our addr2line binary with other tools, I noticed they sometimes output a discriminator, but we don't. For example, for the postgresql benchmark added in #315:

```
0x1c5111
visibilitymap_pin_ok
/usr/src/debug/postgresql-16.3/src/backend/access/heap/visibilitymap.c:221 (discriminator 1)
```
