x86-64: memcpy performance reduce when running in virtual mechine

[Shuo Wang <wangshuo47@huawei.com>]

The performance of memcpy 1024 has recovered. However, there is performance
reduce in host. This is test result (cycle):

	                      memcpy_10	 memcpy_1k	 memcpy_10k	  memcpy_1m	  memcpy_10m
before backport	             8	         34	        187	        130848	   2325409
after backport	             8	         34	        182	        515156	   5282603
Performance improvement	   0.00%	    0.00%	    2.67%	    -293.71%   -127.17%

>* Shuo Wang:
>
>> The environment information is as follows:
>> [host]
>> - kernel version: 4.18.0
>> - glibc version: 2.28
>> - gcc version: 8.3.1
>> - qemu version: 2.12.0
>> - libvirtd version: 4.5.0
>
>Does your have a glibc a backport of this patch?
>
>commit d3c57027470b78dba79c6d931e4e409b1fecfc80
>Author: Patrick McGehearty <patrick.mcgehearty@oracle.com>
>Date:   Mon Sep 28 20:11:28 2020 +0000
>
>    Reversing calculation of __x86_shared_non_temporal_threshold
>
>Some hypervisors set the number of reported threads in CPUID to zero.
>
>Thanks,
>Florian
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