[PATCH v4 2/2] x86_64: roundeven with sse4.1 support

[Florian Weimer]

* H. J. Lu via Libc-alpha:

>> Here is a benchmark result on my AMD Ryzen 9 3900X system:
>
> Since we don't know or may not care SSE4 machines without AVX,
> should we make it to AVX only?

What about Goldmont/Tremont?  Those are current CPUs which do not
support AVX, but I think they have sufficient SSE4 support levels for
this change.

Thanks,
Florian