require et random_device for cons token test

[Jonathan Wakely]

On 24/03/21 13:22 +0000, Koning, Paul via Libstdc++ wrote:
>
>
>> 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.

I'm talking about the C++ std::random_device type, not the /dev/random
block device.

>> 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.

Libstdc++ already contains several PNRGs, we don't need to use
Fortran's.