64 bit time_t on riscv32

[Florian Weimer]

* Adhemerval Zanella Netto:

> My understanding was __USE_TIME_BITS64 would be required only for ABIs
> that actually would multiple time_t sizes and the glibc 64 bit time_t 
> supported was added on this assumption.  However, the design document 
> does state __USE_TIME_BITS64 would be defined even for architectures 
> where is does not require it.  I it was not really caught in development
> because the design creator was not really much involved at the time.
>
> I think it should be feasible to fix it, although backporting it would
> generate a quite large patch.

It will break applications that use __USE_TIME_BITS64 with glibc's
current semantics centered on time64 redirects (incorrectly, of
course—it's an internal macro).  I think the use in the kernel is
probably easier to address, and it has to be changed for compatibility
with other libcs anyway.

Thanks,
Florian