Merge commit '8f863fcd77e1' from llvm.org/main into next

Author: git apple-llvm automerger

.ci/monolithic-linux.sh

@@ -110,7 +110,11 @@ if [[ "${runtimes}" != "" ]]; then
 
   echo "--- cmake runtimes clang modules"
 
-  rm -rf "${RUNTIMES_BUILD_DIR}"
+  # We don't need to do a clean build of runtimes, because LIBCXX_TEST_PARAMS
+  # and LIBCXXABI_TEST_PARAMS only affect lit configuration, which successfully
+  # propagates without a clean build. Other that those two variables, builds
+  # are supposed to be the same.
+
   cmake -S "${MONOREPO_ROOT}/runtimes" -B "${RUNTIMES_BUILD_DIR}" -GNinja \
       -D CMAKE_C_COMPILER="${INSTALL_DIR}/bin/clang" \
       -D CMAKE_CXX_COMPILER="${INSTALL_DIR}/bin/clang++" \