[workflows] Minimal workflow to create an AArch64 container

AArch64 GitHub workflows require a Docker container named after the branch.
This commit adds the minimal workflow required to create the container image
for building and testing subsequent pull requests.

Cherry-picking note: This commit also squashes parts of the following commits
in order to modernize the tools in the Docker image.

    e698fc8 [workflows] Update GitHub actions to use modern tools
    6aeab31 [workflows] Fix GitHub action bugs

Author: bryanpkc

.github/workflows/UbuntuDockerfile

@@ -0,0 +1,59 @@
+FROM ubuntu:22.04
+
+ARG DEBIAN_FRONTEND=noninteractive
+ENV TZ=Europe/London
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install -y \
+      curl \
+      gcc \
+      g++ \
+      make \
+      htop \
+      jq \
+      ninja-build \
+      tmux \
+      git \
+      wget \
+      patch \
+      python3-minimal \
+      python-is-python3 \
+      libdata-dumper-simple-perl \
+      unzip
+
+RUN apt-get install -y software-properties-common && \
+    apt-get update && \
+    add-apt-repository ppa:ubuntu-toolchain-r/test && \
+    apt-get install -f -y gcc-12 g++-12 && \
+    apt-get install -f -y llvm-14 clang-14 && \
+    apt-get install -f -y llvm-15 clang-15
+
+# Install the tools for release_13x and newer
+RUN apt --fix-missing update && \
+    apt install -y build-essential manpages-dev \
+    libssl-dev zlib1g-dev \
+    libbz2-dev libreadline-dev libsqlite3-dev libncurses5-dev && \
+    apt install -y python3-distutils python3-psutil \
+    libncursesw5-dev xz-utils tk-dev libffi-dev liblzma-dev python3-openssl
+
+RUN cd /opt && \
+    wget https://github.com/Kitware/CMake/releases/download/v3.20.0/cmake-3.20.0-linux-aarch64.sh && \
+    /bin/sh cmake-3.20.0-linux-aarch64.sh --skip-license --include-subdir && \
+    ln -s /opt/cmake-3.20.0-linux-aarch64/bin/* /usr/local/bin
+
+RUN ln -s /usr/bin/ninja-build /usr/local/bin/ninja
+
+RUN mkdir /home/github/
+
+ARG BRANCH_NAME
+ARG INITIAL_BUILD
+RUN if [ "$INITIAL_BUILD" != "true" ]; then \
+    mkdir /home/root && cd home/root && \
+    git clone --depth 1 --single-branch --branch $BRANCH_NAME https://github.com/flang-compiler/classic-flang-llvm-project.git classic-flang-llvm-project && \
+    cd classic-flang-llvm-project && \
+    ./build-llvm-project.sh -t AArch64 -p /home/github/usr/local -n `nproc --ignore=1` -a /usr/bin/gcc-12 -b /usr/bin/g++-12 -i -v; \
+    fi
+
+RUN useradd github && \
+    chown -R github:github /home/github
+USER github

.github/workflows/build_push_docker_image_Ubuntu.yml

@@ -0,0 +1,49 @@
+name: Pre-compile llvm ARM64
+
+on:
+  workflow_dispatch:
+    inputs:
+      initialBuild:
+        description: "True if creating an initial Docker image for this branch"
+        required: true
+        type: boolean
+  push:
+    branches:
+      - 'release_*x'
+    paths-include:
+      - '**/.github/workflows/build_push_docker_image_Ubuntu.yml'
+      - '**/.github/workflows/UbuntuDockerfile.yml'
+
+jobs:
+  docker:
+    runs-on: self-hosted
+    steps:
+      - name: Extract branch name
+        run: echo "::set-output name=branch::${GITHUB_REF#refs/heads/}"
+        id: extract_branch
+
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Log in
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          file: .github/workflows/UbuntuDockerfile
+          push: true
+          no-cache: true
+          context: .github/workflows
+          tags: ghcr.io/${{ github.repository_owner }}/ubuntu-flang-${{ steps.extract_branch.outputs.branch }}:latest
+          platforms: linux/arm64
+          build-args: |
+            BRANCH_NAME=${{ steps.extract_branch.outputs.branch }}
+            INITIAL_BUILD=${{ inputs.initialBuild }}