Try building ARM64 Linux package on macOS.

.github/workflows/docker.yaml

@@ -20,10 +20,76 @@ env:
   USER: chevah
   CHEVAH_CONTAINER: yes
 
-# Using a job name that doesn't contain the OS name, to minimize the risk of
-# confusion with the OS names of the containers, which are the relevant ones.
 jobs:
-  latest:
+
+  arm64:
+    runs-on: macos-latest
+    container: amazonlinux-2
+    strategy:
+      fail-fast: false
+
+    timeout-minutes: 30
+    steps:
+    - name: Prepare OS
+      run:  yum -y install git-core gcc make m4 patch tar unzip perl perl-Test-Simple xz gcc-c++ dejagnu
+
+    # On a Docker container, everything runs as root by default.
+    - name: Chevah user setup
+      run: |
+        useradd -g adm -s /bin/bash -m chevah
+        # Don't just add to the file, reset it, as some default options might
+        # be detrimental to our testing, e.g. CentOS 5's "requiretty" option.
+        echo '%adm    ALL=NOPASSWD: ALL' > /etc/sudoers
+
+    # GHA's checkout action doesn't work on exotic platforms. This fails on opening a new PR.
+    - name: Clone sources independently
+      run: |
+        cd /home/chevah/
+        git init $CHEVAH_REPO
+        cd $CHEVAH_REPO
+        # Cleanup the repo.
+        git rev-parse --symbolic-full-name --verify --quiet HEAD || true
+        git rev-parse --symbolic-full-name --branches || true
+        git remote remove origin || true
+        # Update repo token.
+        git remote add origin https://github.com/chevah/$CHEVAH_REPO
+        git fetch --no-tags --prune origin
+        # Prepare the code.
+        git clean -f
+        git reset --hard ${{ github.event.after }}
+        git log -1 --format='%H'
+
+    - name: Detect OS and build Python
+      run: |
+        cd /home/chevah/$CHEVAH_REPO
+        ./brink.sh detect_os
+        ./chevah_build build
+
+    - name: Own tests
+      run: |
+        cd /home/chevah/$CHEVAH_REPO
+        ./chevah_build test
+
+    # Compat tests must run as regular user with sudo rights.
+    - name: Compat tests
+      run: |
+        chown -R chevah /home/chevah/$CHEVAH_REPO
+        cd /home/chevah/$CHEVAH_REPO
+        true su chevah -c "./chevah_build compat"
+
+    # Using `~/` is problematic under Docker, use `/root/`.
+    - name: Upload testing package
+      run: |
+        mkdir -pv /root/.ssh/
+        cd /home/chevah/$CHEVAH_REPO
+        touch priv_key
+        chmod 600 priv_key
+        echo "${{ secrets.SFTPPLUS_BIN_PRIV_KEY }}" > priv_key
+        echo "${{ secrets.SFTPPLUS_BIN_HOST_KEY }}" > /root/.ssh/known_hosts
+        ./publish_dist.sh
+        rm priv_key
+
+  x64:
     runs-on: ubuntu-latest
     container: ${{ matrix.container }}
     strategy: