Allow Specifying the builder image.

This change attempts to shift the libc++ builders over to new backend infrastructure that allows running an arbitrary container for the libc++ job. This has been a long time in the making, and support from github and gke is finally at the point where it's possible (hopefully). This change should also demonstrate another important property: No Downtime Upgrades. If this goes well, we'll be able to test the upgrade as a part of the PR process, and then commiting it to main should (ideally) not break anything.

Author: EricWF

.github/workflows/libcxx-build-and-test.yaml

@@ -49,7 +49,8 @@ env:
 jobs:
  stage1:
  if: github.repository_owner == 'llvm'
- runs-on: libcxx-runners-8-set
+ runs-on: libcxx-runners-set
+ container: ghcr.io/libcxx/actions-builder:testing-2024-09-21
  continue-on-error: false
  strategy:
  fail-fast: false
@@ -84,7 +85,8 @@ jobs:
  **/crash_diagnostics/*
  stage2:
  if: github.repository_owner == 'llvm'
- runs-on: libcxx-runners-8-set
+ runs-on: libcxx-runners-set
+ container: ghcr.io/libcxx/actions-builder:testing-2024-09-21
  needs: [ stage1 ]
  continue-on-error: false
  strategy:
@@ -160,20 +162,21 @@ jobs:
  'benchmarks',
  'bootstrapping-build'
  ]
- machine: [ 'libcxx-runners-8-set' ]
+ machine: [ 'libcxx-runners-set' ]
  include:
  - config: 'generic-cxx26'
- machine: libcxx-runners-8-set
+ machine: libcxx-runners-set
  - config: 'generic-asan'
- machine: libcxx-runners-8-set
+ machine: libcxx-runners-set
  - config: 'generic-tsan'
- machine: libcxx-runners-8-set
+ machine: libcxx-runners-set
  - config: 'generic-ubsan'
- machine: libcxx-runners-8-set
+ machine: libcxx-runners-set
  # Use a larger machine for MSAN to avoid timeout and memory allocation issues.
  - config: 'generic-msan'
- machine: libcxx-runners-8-set
+ machine: libcxx-runners-set
  runs-on: ${{ matrix.machine }}
+ container: ghcr.io/libcxx/actions-builder:testing-2024-09-21
  steps:
  - uses: actions/checkout@v4
  - name: ${{ matrix.config }}