ci(*): add support for LLVM 21 (llvm-build-bump-pr) (#394)

This pull request updates the `.github/workflows/llvm-build-bump-pr.yml`
workflow to improve compatibility and reliability of the build process
across multiple platforms. The main changes involve switching from
custom Ubuntu images to standard Docker images, updating package
installation commands, and adjusting dependency installation steps.

**Platform and Docker image updates:**

* The `matrix.docker` configuration now uses standard Docker images
(`python:3.10.18-bullseye` for ARM and `buildpack-deps:jammy` for PPC64
and S390X) instead of custom Ubuntu images, simplifying image management
and improving consistency across platforms.

**Build and dependency installation changes:**

* All `apt` commands have been replaced with `apt-get` for better
scripting reliability, and package installation steps have been updated
to match the new images.
[[1]](diffhunk://#diff-d608eb75b383338d789a8908995e47499214a7cc55a847771ad73800464b18b0L87-R88)
[[2]](diffhunk://#diff-d608eb75b383338d789a8908995e47499214a7cc55a847771ad73800464b18b0L208-R210)
* The Docker run command now uses the new `image` variable instead of
the deprecated `ubuntu-image`, ensuring the correct image is used for
each platform.
* The dependency installation step inside Docker now installs specific
versions of `cmake` and `pyinstaller` via `pip`, and removes unnecessary
packages (`git`, `g++`).

**Workflow variable and debug updates:**

* Debug output and Docker run commands have been updated to use the new
`image` variable instead of `ubuntu-image`, reflecting the changes in
the matrix configuration.
[[1]](diffhunk://#diff-d608eb75b383338d789a8908995e47499214a7cc55a847771ad73800464b18b0L187-R187)
[[2]](diffhunk://#diff-d608eb75b383338d789a8908995e47499214a7cc55a847771ad73800464b18b0L197-R197)

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>

Author: lumirlumir

.github/workflows/llvm-build-bump-pr.yml

@@ -84,8 +84,8 @@ jobs:
 
       - name: Set up dependencies
         run: |
-          sudo apt update -y
-          sudo apt install -y ninja-build
+          sudo apt-get update -y
+          sudo apt-get install -y ninja-build
           pip install pyinstaller
 
       - name: Set up checkout
@@ -164,16 +164,16 @@ jobs:
       matrix:
         docker:
           - platform: arm/v7
-            ubuntu-image: arm32v7
+            image: python:3.10.18-bullseye
             node-name: arm
           - platform: arm64/v8
-            ubuntu-image: arm64v8
+            image: python:3.10.18-bullseye
             node-name: arm64
           - platform: ppc64le
-            ubuntu-image: ppc64le
+            image: buildpack-deps:jammy
             node-name: ppc64
           - platform: s390x
-            ubuntu-image: s390x
+            image: buildpack-deps:jammy
             node-name: s390x
 
     runs-on: ubuntu-22.04
@@ -184,7 +184,7 @@ jobs:
 
     steps:
       - name: Debug matrix
-        run: echo ${{ matrix.docker.platform }} ${{ matrix.docker.ubuntu-image }} ${{ matrix.docker.node-name }}
+        run: echo ${{ matrix.docker.platform }} ${{ matrix.docker.image }} ${{ matrix.docker.node-name }}
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
@@ -194,7 +194,7 @@ jobs:
       # Use the oldest ubuntu image version possible for backward compatibility.
       - name: Docker run
         run: |
-          docker run --name ${{ matrix.docker.node-name }} --platform linux/${{ matrix.docker.platform }} ${{ matrix.docker.ubuntu-image }}/ubuntu:22.04 /bin/bash -c "
+          docker run --name ${{ matrix.docker.node-name }} --platform linux/${{ matrix.docker.platform }} ${{ matrix.docker.image }} /bin/bash -c "
             echo ---Set up environment variables--- &&
             export DEBIAN_FRONTEND=noninteractive &&
 
@@ -205,9 +205,9 @@ jobs:
             pwd &&
 
             echo ---Set up dependencies--- &&
-            apt update -y &&
-            apt install -y git python3 python3-pip g++ cmake ninja-build &&
-            pip install pyinstaller &&
+            apt-get update -y &&
+            apt-get install -y python3 python3-pip ninja-build &&
+            pip install cmake==3.31.6 pyinstaller &&
 
             echo ---Set up checkout--- &&
             git clone --depth 1 --branch ${{ needs.stage1.outputs.LLVM_LATEST_RELEASE_TAG_NAME }} https://github.com/${{ env.LLVM_REPO }}.git &&