[llvm] [workflows] Build a container for running CI on github actions (PR #75286)

[Tom Stellard via llvm-commits]

================
@@ -0,0 +1,51 @@
+
+name: Build CI Container
+
+permissions:
+  contents: read
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - .github/workflows/build-ci-container.yml
+      - '.github/workflows/containers/github-action-ci/**'
+  pull_request:
+    branches:
+      - main
+    paths:
+      - .github/workflows/build-ci-container.yml
+      - '.github/workflows/containers/github-action-ci/**'
+
+jobs:
+  build-ci-container:
+    if: github.repository_owner == 'llvm'
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - name: Write Variables
+        id: vars
+        run: |
+          echo "container-name=ghcr.io/$GITHUB_REPOSITORY_OWNER/ci-ubuntu-22.04" >> $GITHUB_OUTPUT
+
+      - name: Checkout LLVM
+        uses: actions/checkout at v4
+
+      - name: Build Container
+        working-directory: ./.github/workflows/containers/github-action-ci/
+        run: |
+          # TODO: Ideally, we would give each container build a unique name,
+          # but we have limited space in the container registry, so we can't
----------------
tstellar wrote:

> Do you have a source for this? I believe this falls under Github packages, which should be free for public packages.
> 
> It also seems like they don't have any billing setup for the container registry for even enterprise accounts.
> 

OK, I missed that the limits only applied to private packages.

> Tagging with the short SHA and then also tagging the image as `latest` would probably be good. There should be a way to just push the tag as well without having to push the image twice. This might be something for a follow up patch though.

I will look into this.

https://github.com/llvm/llvm-project/pull/75286