docker: build linux/arm64 images (#398)

.github/workflows/docker.yml

@@ -69,3 +69,46 @@ jobs:
       - name: Inspect Docker images
         run: |
           docker images
+
+  docker-build-toolchain:
+    needs: [prepare]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ (inputs.commit != '' && inputs.commit) || inputs.branch }}
+      - name: Download toolchain
+        uses: dawidd6/action-download-artifact@v3
+        with:
+          workflow: build.yml
+          workflow_conclusion: success
+          commit: ${{inputs.commit}}
+          branch: ${{inputs.branch}}
+          event: push
+          name: linux-ucrt-.*
+          name_is_regexp: true
+          path: toolchain
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Log in to Docker Hub
+        if: ${{inputs.login}}
+        uses: docker/login-action@v3
+        with:
+          username: ${{secrets.DOCKER_USERNAME}}
+          password: ${{secrets.DOCKER_PASSWORD}}
+      - name: Build Docker images
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/arm64
+          push: ${{inputs.push}}
+          file: ./Dockerfile.toolchain
+          load: true
+          tags: |
+            mstorsjo/llvm-mingw:latest
+            mstorsjo/llvm-mingw:${{needs.prepare.outputs.TAG}}
+      - name: Inspect Docker images
+        run: |
+          docker images