[PATCH] ntdll: Only use sysinfo function when present

[Gerald Pfeifer]

On Tue, 10 Aug 2021, Gerald Pfeifer wrote:
> On some systems <sys/sysinfo.h> may be present while the sysinfo
> function may not, or at least not as part of standard libraries,
> so check whether the function is actually available before using
> it.

Note that the Marvin tester complained about test failures, which I
believe is only due to me not including changes to generated files
(autoconf, which show unrelated differences due to different versions
of autoconf).

I assume/hope Alexandre is simply running autoconf after applying
this patch (and then hopefully pushing everything)? :-)

Thanks,
Gerald