github: Build the whole multiplatform docker image with Dockerfile.toolchain

This reverts commit 8f42112,
and fixes building the multiplatform image in a simpler way.

Instead of doing two separate builds, with separate Dockerfiles,
just do one multiplatform build of one Dockerfile, which
docker runs serially, for each one of the included architectures.

Author: mstorsjo

.github/workflows/docker.yml

@@ -64,18 +64,11 @@ jobs:
   docker-build:
     needs: [prepare]
     runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - { file: Dockerfile, key: amd64 }
-          - { file: Dockerfile.toolchain, platforms: linux/arm64, key: arm64 }
     steps:
       - uses: actions/checkout@v4
         with:
           ref: ${{inputs.ref}}
       - name: Download toolchain
-        if: ${{matrix.file == 'Dockerfile.toolchain'}}
         uses: dawidd6/action-download-artifact@v10
         with:
           workflow: build.yml
@@ -86,7 +79,6 @@ jobs:
           name_is_regexp: true
           path: toolchain
       - name: Set up QEMU
-        if: ${{matrix.file == 'Dockerfile.toolchain'}}
         uses: docker/setup-qemu-action@v3
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -98,42 +90,15 @@ jobs:
           password: ${{secrets.DOCKER_PASSWORD}}
       - name: Build Docker images
         uses: docker/build-push-action@v5
-        id: build
         with:
           context: .
-          platforms: ${{matrix.platforms}}
+          platforms: linux/amd64,linux/arm64
           push: ${{inputs.push}}
-          file: ./${{matrix.file}}
-          outputs: |
-            type=image,name=mstorsjo/llvm-mingw,push-by-digest=true,name-canonical=true
-      - name: Write outputs for later steps
-        uses: cloudposse/github-action-matrix-outputs-write@main
-        id: out
-        with:
-          matrix-step-name: ${{github.job}}
-          matrix-key: ${{matrix.key}}
-          outputs: |-
-            digest: ${{steps.build.outputs.digest}}
-
-  docker-create:
-    needs: [docker-build, prepare]
-    runs-on: ubuntu-latest
-    if: ${{inputs.push}}
-    steps:
-      - uses: cloudposse/github-action-matrix-outputs-read@main
-        id: read
-        with:
-          matrix-step-name: docker-build
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{vars.DOCKER_USERNAME}}
-          password: ${{secrets.DOCKER_PASSWORD}}
-      - name: Create final image
+          file: ./Dockerfile.toolchain
+          load: ${{!inputs.push}}
+          tags: |
+            mstorsjo/llvm-mingw:latest
+            mstorsjo/llvm-mingw:${{needs.prepare.outputs.TAG}}
+      - name: Inspect Docker images
         run: |
-          set -x
-          for tag in latest ${{needs.prepare.outputs.TAG}}; do
-              docker buildx imagetools create -t mstorsjo/llvm-mingw:$tag mstorsjo/llvm-mingw@${{fromJson(steps.read.outputs.result).digest.amd64}} mstorsjo/llvm-mingw@${{fromJson(steps.read.outputs.result).digest.arm64}}
-          done
+          docker images