[PATCH] Add getcpu

[Florian Weimer]

* H. J. Lu:

> I updated the patch with a very simple test.

The simple test has a race condition unfortunately.

I think we could fold the test into the existing affinity tests.

The main question is whether getcpu is fast enough.  It does not perform
a system call, but in my tests a while back, it was still rather slow.

The new rseq-based getcpu does not support NUMA nodes, it seems.  Maybe
it's still possible to fix that.

Thanks,
Florian