time64 functions for glibc

[Paul Eggert]

On 6/23/21 9:59 AM, Joseph Myers wrote:
>> -* Add support for 64 bit time_t for ABIs with defaults to 32 bit time_t.
>> +* Add support for 64 bit time_t for ABIs with defaults currently unchanged.

> I think the intended meaning of this was that "ABIs with defaults to 32
> bit time_t" was a phrase describing those glibc configurations for which
> support for 64-bit time_t was added

Oh, that intended meaning wasn't clear to me. How about if we change 
that sentence to the following, which I hope makes things clearer.

* Add support for 64-bit time_t on configurations like x86 where time_t
   is traditionally 32-bit.  Although time_t still defaults to 32-bit on
   these configurations, this default may change in future versions.