[llvm] [libcxx] Add libc++ github actions workflow to replace buildkite (PR #71836)

[via llvm-commits]

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@@ -0,0 +1,112 @@
+name: Build and Test libc++
+
+on: pull_request
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+
+env:
+  CMAKE: "/opt/bin/cmake"
+
+# Comment
+jobs:
+  stage1:
+    runs-on: libcxx-runners-16
+    continue-on-error: false
+    strategy:
+      fail-fast: true
+      matrix:
+        config: [ 'generic-cxx26', 'generic-cxx03', 'generic-modules' ]
+        cc: [ 'clang-18' ]
+        cxx: [ 'clang++-18' ]
+        include:
+          - config: 'generic-gcc'
+            cc: 'gcc-13'
+            cxx: 'g++-13'
+    steps:
+      - uses: actions/checkout at v4
+      - name: ${{ matrix.config }}.${{ matrix.cxx }}
+        run: libcxx/utils/ci/run-buildbot ${{ matrix.config }}
+        env:
+          CC: ${{ matrix.cc }}
+          CXX: ${{ matrix.cxx }}
+      - uses: actions/upload-artifact at v3
+        if: always()
+        with:
+          name: ${{ matrix.config }}-${{ matrix.cxx }}-results
+          path: |
+            "**/test-results.xml"
+            "**/*.abilist"
+  stage2:
+    runs-on: libcxx-runners-8
+    needs: [ stage1  ]
+    continue-on-error: false
+    strategy:
+      fail-fast: true
----------------
EricWF wrote:

Outside of stage 1 and 2 I believe. 

https://github.com/llvm/llvm-project/pull/71836