diff --git a/clang/utils/ci/run-buildbot b/clang/utils/ci/run-buildbot
--- a/clang/utils/ci/run-buildbot
+++ b/clang/utils/ci/run-buildbot
@@ -60,6 +60,10 @@
 BUILD_DIR="${BUILD_DIR:=${MONOREPO_ROOT}/build/${BUILDER}}"
 INSTALL_DIR="${BUILD_DIR}/install"
 
+function clean() {
+    rm -rf "${BUILD_DIR}"
+}
+
 # Print the version of a few tools to aid diagnostics in some cases
 cmake --version
 ninja --version
@@ -95,7 +99,17 @@
     export CC=$(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 "${BUILD_DIR}" check-runtimes
 ;;
 generic-cxx26)
     buildkite-agent artifact download install.tar.xz .
@@ -103,7 +117,17 @@
     export CC=$(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 "${BUILD_DIR}" check-runtimes
 ;;
 generic-modules)
     buildkite-agent artifact download install.tar.xz .
@@ -111,7 +135,17 @@
     export CC=$(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.