require et random_device for cons token test

[Koning, Paul]

> On Mar 24, 2021, at 4:59 AM, Jonathan Wakely via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> On 24/03/21 03:53 -0300, Alexandre Oliva wrote:
>> 
>> On target systems that don't support any random_device, not even the
>> default one,
> 
> It should be impossible to have no random_device.

Not true; deeply embedded systems might not have one.  Among GCC platforms, pdp11 doesn't have one, and at least some vax platforms probably don't either.

> As a fallback a
> pseudo random number generator should be used.

Presumably yes -- it seems unlikely that GCC tests depend on cryptographic strength of the random nummber generator.  If a PRNG is used then the classic FORTRAN "random" function would serve.  

	paul