[PATCH] Implement non-trivial std::random_device::entropy (PR libstdc++/67578)

[Jonathan Wakely]

On 22/05/17 22:10 +0800, Xi Ruoyao wrote:
>In very old Linux kernel (1.3.x) there is random.h but not RNDGETENTCNT.
>The random.h without RNDGETENTCNT was only used in the kernel internally.
>But at that time Linux Makefile didn't have "headers_install" target
>so user may copy all headers (including the internal ones) to /usr/include.
>It seems we should check RNDGETENTCNT explicitly if we want to support
>1.3.x.

OK, I think that's ancient enough that we don't need to care about it,
but on the other hand it's not impossible to believe that somebody
could be using a custom Linux kernel that removed it. So let's keep
the test for it.