[libcxx] Install runner last when building CI containers

This patch changes when we install the GHA runner in the CI containers. Instead
of having it in the base image, we install it last. This will enable a follow up
patch that will do some setup enabling building the full container image with an
existing base image, thus enabling updating the GHA runner without modifying the
important bits.

Reviewers: EricWF, ldionne

Reviewed By: ldionne

Pull Request: #148072

Author: boomanaiden154

libcxx/utils/ci/Dockerfile

@@ -311,5 +311,18 @@ CMD /opt/android/container-setup.sh && buildkite-agent start
 #
 FROM builder-base AS actions-builder
 
-WORKDIR /home/runner
-USER runner
+ARG GITHUB_RUNNER_VERSION
+
+RUN useradd gha -u 1001 -m -s /bin/bash
+RUN adduser gha sudo
+RUN echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
+WORKDIR /home/gha
+USER gha
+
+ENV RUNNER_MANUALLY_TRAP_SIG=1
+ENV ACTIONS_RUNNER_PRINT_LOG_TO_STDOUT=1
+RUN mkdir actions-runner && \
+    cd actions-runner && \
+    curl -O -L https://github.com/actions/runner/releases/download/v$GITHUB_RUNNER_VERSION/actions-runner-linux-x64-$GITHUB_RUNNER_VERSION.tar.gz && \
+    tar xzf ./actions-runner-linux-x64-$GITHUB_RUNNER_VERSION.tar.gz && \
+    rm ./actions-runner-linux-x64-$GITHUB_RUNNER_VERSION.tar.gz

libcxx/utils/ci/docker-compose.yml

@@ -10,7 +10,8 @@ services:
       dockerfile: Dockerfile
       target: actions-builder
       args:
-        BASE_IMAGE: ghcr.io/actions/actions-runner:2.326.0
+        BASE_IMAGE: ubuntu:jammy
+        GITHUB_RUNNER_VERSION: "2.326.0"
         <<: *compiler_versions
 
   android-buildkite-builder: