Builder fails when building `FROM scratch` and `ARG` is the second line in Dockerfile

Description

Build is failing with the following error

failed to get destination image "sha256:d713c98f66880c8411b0d55a019d6aac2f45cfc57a48eae50701610d7e3ecf56": image with reference sha256:d713c98f66880c8411b0d55a019d6aac2f45cfc57a48eae50701610d7e3ecf56 was found but does not match the specified platform: wanted linux/arm/v6, actual: linux/amd64

Reproduce

Given a Dockerfile

FROM scratch

ARG myArg
ADD files-${myArg}.tar.gz /

Start a build with docker build --platform=linux/arm/v6 --build-arg myArg=some -t myImg .

Yeilds following output:

docker build --platform=linux/arm/v6 --build-arg myArg=some -t myImg .
Sending build context to Docker daemon  29.67MB
Step 1/13 : FROM scratch
 ---> 
Step 2/13 : ARG myArg
 ---> Running in 06d61fdbc7b5
Removing intermediate container 06d61fdbc7b5
 ---> d713c98f6688
Step 3/13 : ADD files-${myArg}.tar.gz /
failed to get destination image "sha256:d713c98f66880c8411b0d55a019d6aac2f45cfc57a48eae50701610d7e3ecf56": image with reference sha256:d713c98f66880c8411b0d55a019d6aac2f45cfc57a48eae50701610d7e3ecf56 was found but does not match the specified platform: wanted linux/arm/v6, actual: linux/amd64

Adding --no-chache does not change anything.

Now, let's add some command before ARG

Dockerfile

FROM scratch

ADD qwe /

ARG myArg
ADD files-${myArg}.tar.gz /

docker build --platform=linux/arm/v6 --build-arg myArg=some -t myImg .
Sending build context to Docker daemon  29.67MB
Step 1/4 : FROM scratch
 ---> 
Step 2/4 : ADD qwe /
 ---> 4ed4fd43b443
Step 3/4 : ARG myArg
 ---> [Warning] The requested image's platform (linux/arm/v6) does not match the detected host platform (linux/amd64) and no specific platform was requested
 ---> Running in cc1b822df5aa
Removing intermediate container cc1b822df5aa
 ---> 0b548c74b5cc
Step 4/4 : ADD files-${myArg}.tar.gz /
 ---> 891efb6b6913
Successfully built 891efb6b6913
Successfully tagged myImg

Expected behavior

docker build should not fail

docker version

Client:
 Version:           20.10.5+dfsg1
 API version:       1.41
 Go version:        go1.15.15
 Git commit:        55c4c88
 Built:             Mon May 30 18:34:49 2022
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server:
 Engine:
  Version:          20.10.5+dfsg1
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.15.15
  Git commit:       363e9a8
  Built:            Mon May 30 18:34:49 2022
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.13~ds1
  GitCommit:        1.4.13~ds1-1~deb11u4
 runc:
  Version:          1.0.0~rc93+ds1
  GitCommit:        1.0.0~rc93+ds1-5+deb11u2
 docker-init:
  Version:          0.19.0
  GitCommit:

docker info

Client:
 Context:    default
 Debug Mode: false

Server:
 Containers: 2
  Running: 0
  Paused: 0
  Stopped: 2
 Images: 54
 Server Version: 20.10.5+dfsg1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: runc io.containerd.runc.v2 io.containerd.runtime.v1.linux
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 1.4.13~ds1-1~deb11u4
 runc version: 1.0.0~rc93+ds1-5+deb11u2
 init version: 
 Security Options:
  apparmor
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.10.0-23-amd64
 Operating System: Debian GNU/Linux 11 (bullseye)
 OSType: linux
 Architecture: x86_64
 CPUs: 4
 Total Memory: 7.761GiB
 Name: debian
 ID: QDFR:I4CX:AVE2:NJ5Q:LGOQ:VQCA:JGY2:7VVC:HJIW:UOJL:224W:LVV7
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: Support for cgroup v2 is experimental

Additional Info

Same issue is being described here https://github.com/docker/docker-py/issues/2990

Reproduce the failure with the two Dockerfile examples and the docker build command using --platform=linux/arm/v6 and --build-arg. Start by tracing builder handling of ARG after FROM scratch, ADD, and platform metadata, comparing the failing and succeeding Dockerfiles. Done means the original Dockerfile builds successfully for the requested platform without requiring an extra command before ARG.