[Bug libstdc++/85494] implementation of random_device on mingw is useless

[mimomorin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85494

--- Comment #15 from Michel Morin <mimomorin at gmail dot com> ---
> Backporting to stable branches should not be done as a way to find bugs.

Makes sense. I stand corrected.

> The patch affects all targets, not just the ones currently using a PRNG, so it's not as simple as just saying it must be better.

Ah, I didn't notice that.

> I'm afraid you aren't making a very good case for backporting it.

I just felt that waiting for GCC-10 (i.e. about a year) is a bit too long.
(Some of my colleagues suffer from this issue; so I hoped that this fix gets
released earlier... but anyway, I'll probably provide them a wrapper to
workaround the issue.)