[Bug target/126935] [17 Regression] SVE2 incorrectly detected on aarch64 vm

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126935

--- Comment #4 from Drea Pinski <pinskia at gcc dot gnu.org> ---
(In reply to ktkachov from comment #3)
> (In reply to Drea Pinski from comment #2)
> > Actually I think the better check is if the processor has SVE and SVE2.
> > Even though SVE2 should be enough here; it seems like some VMs advertise
> > SVE2 but not SVE support (which in itself odd but that ever).
> 
> Oof, SVE2 but not SVE is a nonsense configuration.
> Anyway, for the libcpp fast-path I've added I think we can make the
> configure check also execute the SVE2 instructions required, not just test
> their HWCAPs. That would sidestep the dodgy VM advertising

But then that would break cross.