[Bug debug/59161] GDB pretty printers: iterator->reference not printed

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59161

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I've forced the relevant printers to convert to a string explicitly, so now you
always get the address, which seems better than {ref = }

So I think the libstdc++ part is fixed, do we want a GDB bug to consider
changing how reference members are displayed? (I think printing the value as
well as the address makes sense).