[libc++] Reorganize and fix the libc++ CI dockerfiles

Instead of having one large Dockerfile building multiple images
with relatively confusing inheritance, explicitly have three
standalone Dockerfiles each building one image. Then, tie the
three images together using the docker-compose file which explicitly
versions the base image used by the Android and the Github Actions
images.

Author: ldionne

.github/workflows/libcxx-build-containers.yml

@@ -15,11 +15,11 @@ on:
     branches:
       - main
     paths:
-      - 'libcxx/utils/ci/**'
+      - 'libcxx/utils/ci/docker/**'
       - '.github/workflows/libcxx-build-containers.yml'
   pull_request:
     paths:
-      - 'libcxx/utils/ci/**'
+      - 'libcxx/utils/ci/docker/**'
       - '.github/workflows/libcxx-build-containers.yml'
 
 jobs:
@@ -40,17 +40,18 @@ jobs:
         echo '{ "data-root": "/mnt/docker" }' | sudo tee /etc/docker/daemon.json
         sudo systemctl restart docker
 
-    - name: Build the Linux builder image
-      working-directory: libcxx/utils/ci
-      run: |
-        docker compose build builder-base
-        docker compose build actions-builder
+    - name: Build the base image
+      run: docker compose --file libcxx/utils/ci/docker/docker-compose.yml build libcxx-builder-base
+      env:
+        TAG: ${{ github.sha }}
+
+    - name: Build the Linux Github Actions image
+      run: docker compose --file libcxx/utils/ci/docker/docker-compose.yml build libcxx-linux-builder
       env:
         TAG: ${{ github.sha }}
 
     - name: Build the Android builder image
-      working-directory: libcxx/utils/ci
-      run: docker compose build android-buildkite-builder
+      run: docker compose --file libcxx/utils/ci/docker/docker-compose.yml build android-buildkite-builder
       env:
         TAG: ${{ github.sha }}
 
@@ -61,19 +62,6 @@ jobs:
         username: ${{ github.actor }}
         password: ${{ secrets.GITHUB_TOKEN }}
 
-    - name: Push the Linux builder image
-      if: github.event_name == 'push'
-      working-directory: libcxx/utils/ci
-      run: |
-        docker compose push builder-base
-        docker compose push actions-builder
-      env:
-        TAG: ${{ github.sha }}
-
-    - name: Push the Android builder image
+    - name: Push the images
       if: github.event_name == 'push'
-      working-directory: libcxx/utils/ci
-      run: |
-        docker compose push android-buildkite-builder
-      env:
-        TAG: ${{ github.sha }}
+      run: docker compose push libcxx-builder-base libcxx-linux-builder android-buildkite-builder