diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index baf4707c3169d..c781310d88f33 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -64,12 +64,12 @@ MONOREPO_ROOT="${MONOREPO_ROOT:="$(git rev-parse --show-toplevel)"}"
 BUILD_DIR="${BUILD_DIR:=${MONOREPO_ROOT}/build/${BUILDER}}"
 INSTALL_DIR="${BUILD_DIR}/install"
 
-# On macOS, fall back to using the Ninja provided with Xcode if no other Ninja can be found.
-if which ninja &>/dev/null; then
-    NINJA="$(which ninja)"
-else
-    NINJA="$(xcrun --find ninja)"
-fi
+# If we can find Ninja/CMake provided by Xcode, use those since we know their
+# version will generally work with the Clang shipped in Xcode (e.g. if Clang
+# knows about -std=c++20, the CMake bundled in Xcode will probably know about
+# that flag too).
+if xcrun --find ninja &>/dev/null; then NINJA="$(xcrun --find ninja)"; else NINJA="ninja"; fi
+if xcrun --find cmake &>/dev/null; then CMAKE="$(xcrun --find cmake)"; else CMAKE="cmake"; fi
 
 function clean() {
     rm -rf "${BUILD_DIR}"
@@ -77,7 +77,7 @@ function clean() {
 
 function generate-cmake-base() {
     echo "--- Generating CMake"
-    cmake \
+    ${CMAKE} \
           -B "${BUILD_DIR}" \
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
@@ -141,7 +141,7 @@ function check-cxx-benchmarks() {
 }
 
 # Print the version of a few tools to aid diagnostics in some cases
-cmake --version
+${CMAKE} --version
 ${NINJA} --version
 
 case "${BUILDER}" in
@@ -403,7 +403,8 @@ unified-standalone)
     clean
 
     echo "--- Generating CMake"
-    cmake -S "${MONOREPO_ROOT}/libcxx/utils/ci/runtimes" \
+    ${CMAKE} \
+          -S "${MONOREPO_ROOT}/libcxx/utils/ci/runtimes" \
           -B "${BUILD_DIR}" \
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
@@ -419,9 +420,10 @@ runtimes-build)
     clean
 
     echo "--- Generating CMake"
-    cmake -S "${MONOREPO_ROOT}/llvm" \
+    ${CMAKE} \
+          -S "${MONOREPO_ROOT}/llvm" \
           -B "${BUILD_DIR}" \
-          -GNinja \
+          -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
           -DLLVM_ENABLE_PROJECTS="clang" \
@@ -441,7 +443,8 @@ legacy-standalone)
     clean
 
     echo "--- Generating CMake"
-    cmake -S "${MONOREPO_ROOT}/libcxx" \
+    ${CMAKE} \
+          -S "${MONOREPO_ROOT}/libcxx" \
           -B "${BUILD_DIR}/libcxx" \
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
@@ -451,7 +454,8 @@ legacy-standalone)
           -DLIBCXX_CXX_ABI_INCLUDE_PATHS="${MONOREPO_ROOT}/libcxxabi/include" \
           -DLIBCXX_CXX_ABI_LIBRARY_PATH="${BUILD_DIR}/libcxxabi/lib"
 
-    cmake -S "${MONOREPO_ROOT}/libcxxabi" \
+    ${CMAKE} \
+          -S "${MONOREPO_ROOT}/libcxxabi" \
           -B "${BUILD_DIR}/libcxxabi" \
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \