[clang] Fix the pre-commit CI pipeline after changes to libc++'s own CI pipeline

[ldionne]

Summary

We made some changes to the libc++ CI pipeline that take for granted
that we're running on libc++'s own Docker images. This was necessary for
a temporary period until widely-used tools update to a version that can
handle C++20 modules.

However, this had the unintended consequence of breaking the Clang CI
pipeline, which used the libc++ CI scripts as an implementation detail.
Instead, decouple the Clang CI pipeline from the libc++ build scripts.

[ldionne]

Along with aa60b2687ce3b67e454ba7c8c58a8688247df0b8, this will make the Clang CI green again. We'll figure out what's the underlying cause for aa60b2687ce3b67e454ba7c8c58a8688247df0b8 tomorrow, it's too late for today.

[ldionne]

The follow-up to the temporary workaround is going to be done tomorrow in D158694.

clang/utils/ci/run-buildbot

case ${1} in
             ;;
     esac
 done
 
 MONOREPO_ROOT="${MONOREPO_ROOT:="$(git rev-parse --show-toplevel)"}"
 BUILD_DIR="${BUILD_DIR:=${MONOREPO_ROOT}/build/${BUILDER}}"
 INSTALL_DIR="${BUILD_DIR}/install"
 
+function clean() {
+    rm -rf "${BUILD_DIR}"
+}
+
 # Print the version of a few tools to aid diagnostics in some cases
 cmake --version
 ninja --version
 
 case "${BUILDER}" in
 check-format)
     ! grep -rnI '[[:blank:]]$' clang/lib clang/include clang/docs
 ;;
build-clang)
     buildkite-agent artifact upload --debug install.tar.xz
 ;;
 generic-cxx03)
     buildkite-agent artifact download install.tar.xz .
     tar -xvf install.tar.xz
     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
+
+    clean
+    cmake -S "${MONOREPO_ROOT}/runtimes" -B "${BUILD_DIR}" -GNinja \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
+          -DLIBCXX_CXX_ABI=libcxxabi \
+          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+          -DLIBCXX_TEST_PARAMS="std=c++03" \
+          -DLIBCXXABI_TEST_PARAMS="std=c++03"
+
+    ninja -vC "${BUILD_DIR}" check-runtimes
 ;;
 generic-cxx26)
     buildkite-agent artifact download install.tar.xz .
     tar -xvf install.tar.xz
     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-cxx26
+
+    clean
+    cmake -S "${MONOREPO_ROOT}/runtimes" -B "${BUILD_DIR}" -GNinja \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
+          -DLIBCXX_CXX_ABI=libcxxabi \
+          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+          -DLIBCXX_TEST_PARAMS="std=c++26" \
+          -DLIBCXXABI_TEST_PARAMS="std=c++26"
+
+    ninja -vC "${BUILD_DIR}" check-runtimes
 ;;
 generic-modules)
     buildkite-agent artifact download install.tar.xz .
     tar -xvf install.tar.xz
     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
+
+    clean
+    cmake -S "${MONOREPO_ROOT}/runtimes" -B "${BUILD_DIR}" -GNinja \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
+          -DLIBCXX_CXX_ABI=libcxxabi \
+          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+          -DLIBCXX_TEST_PARAMS="enable_modules=clang" \
+          -DLIBCXXABI_TEST_PARAMS="enable_modules=clang"
+
+    ninja -vC "${BUILD_DIR}" check-runtimes
 ;;
 #################################################################
 # Insert vendor-specific internal configurations below.
 #
 # This allows vendors to extend this file with their own internal
 # configurations without running into merge conflicts with upstream.
 #################################################################
 
 #################################################################
 *)
     echo "${BUILDER} is not a known configuration"
     exit 1
 ;;
 esac