(searched for duplicates, couldn't find one).

Description
Original issue from docker/buildx#238.

Looking to build images on my amd64 system for my aarch64 raspberry pi systems. When containerd is detecting my system arch, it is looking for a label in /proc/cpuinfo that does not exist.

Steps to reproduce the issue:

1. Install docker and buildx (https://github.com/docker/buildx/releases)
   Can't remember precisely how I installed docker, but for this issue i don't think it matters.
   Installed buildx by downloading linux-amd64 release and plopping at ~/.docker/cli-plugins/buildx.
   Set "experimental": "enabled" in ~/.docker/config.json
2. Run any buildx command
   ~$ docker buildx ls

Describe the results you received:
Error printed to stderr:
ERRO[0000] failure getting variant error="getCPUInfo for pattern: Cpu architecture: not found"
NAME/NODE DRIVER/ENDPOINT STATUS PLATFORMS
default * docker
default default running linux/amd64, linux/386

Describe the results you expected:
No error printed.

Output of containerd --version:
OS: Kubuntu 19.10
Docker version 19.03.2, build 6a30dfca03
containerd github.com/containerd/containerd 1.3.3-0ubuntu1~19.10.1

Any other relevant information:
It seems as this is only a cosmetic error, commands seem to execute just fine. Seeing as how it later detects "linux/amd64", somewhere else it is clearly able to get amd64.

Top of stack likely https://github.com/containerd/containerd/blob/master/platforms/cpuinfo.go#L93.

In a preliminary check, it looks like container is looking for a label "Cpu architecture" in /proc/cpuinfo? This label does not in /proc/cpuinfo on my system (which is effectively stock).
cat /proc/cpuinfo | grep -i "architecture" | wc -l => 0

amd64 is nowhere to be found in this file. maybe doing whatever lscpu is doing, very first line is Architecture: x86_64