[ci] Run the Clang pre-commit CI on the Debian runners

[ldionne]

Summary

This is to avoid using the libc++ CI resources for running CI on Clang
patches. Libc++'s own CI has seen a large spike in turnaround time since
we have started sharing our resources with the Clang CI due to the large
number of Clang patches. This is an attempt to mitigate that.

[Mordante]

Thanks for working on this! I noticed the additional load on the libc++ CI too.

[ldionne]

This was actually done in D157324.

libcxx/utils/ci/buildkite-pipeline-clang.yml

commands:
       - "mkdir install"
       - "cmake -S llvm -B build -G Ninja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=install -DLLVM_ENABLE_PROJECTS=\"clang;compiler-rt\""
       - "ninja -C build install-clang install-clang-resource-headers"
       - "buildkite-agent artifact upload 'install/**/*'"
     env:
         CC: "clang-${LLVM_HEAD_VERSION}"
         CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
-      queue: "libcxx-builders"
-      os: "linux"
+      queue: "linux" # Use the Clang CI resources for this
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - wait
 
   - label: "C++03"
     commands:
       - "buildkite-agent artifact download 'install/**' ."
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-cxx03"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env:
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}" # TODO: Should we build that from scratch?
         CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
-      queue: "libcxx-builders"
-      os: "linux"
+      queue: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - label: "C++2b"
     commands:
       - "buildkite-agent artifact download 'install/**' ."
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-cxx2b"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env:
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}" # TODO: Should we build that from scratch?
         CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
-      queue: "libcxx-builders"
-      os: "linux"
+      queue: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - label: "Modules"
     commands:
       - "buildkite-agent artifact download 'install/**' ."
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-modules"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env:
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}" # TODO: Should we build that from scratch?
         CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
-      queue: "libcxx-builders"
-      os: "linux"
+      queue: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120

libcxx/utils/ci/generate-buildkite-pipeline

 if git diff --name-only HEAD~1 | grep -q -E "^libcxx/|^libcxxabi/|^libunwind/|^runtimes/|^cmake/"; then
   LIBCXX_CHANGED=true
 fi
 
 if git diff --name-only HEAD~1 | grep -q -E "^clang/"; then
   CLANG_CHANGED=true
 fi
 
-if [[ "${CLANG_CHANGED}" == "true" && "${LIBCXX_CHANGED}" != "true" ]]; then
-  cat libcxx/utils/ci/buildkite-pipeline-clang.yml
-else
-  cat libcxx/utils/ci/buildkite-pipeline.yml
-fi
+# TEMPORARY FOR TESTING
+
+# if [[ "${CLANG_CHANGED}" == "true" && "${LIBCXX_CHANGED}" != "true" ]]; then
+#   cat libcxx/utils/ci/buildkite-pipeline-clang.yml
+# else
+#   cat libcxx/utils/ci/buildkite-pipeline.yml
+# fi