[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 #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Brecht Sanders from comment #5)
> How do I build the core Rust library with/for gccrs ?

That is not currently supported.