[Bug rust/124233] [16 Regression] MinGW-w64 gcc/rust build issues due to missing open_memstream() since r16-2986

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124233

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> ```
> static std::string
> generate_tree_str (tree value)
> {
>   pretty_printer pp;
>   dump_generic_node (&pp, t, 0, flags, true);

dump_generic_node (&pp, value, 0, TDF_NONE, true);


>   std::string result = pp_formatted_text (&pp);
> 
>   if (!result.empty () && result.back () == '\n')
>     result.pop_back ();
> 
>   return result;
> }
> ```