reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install arm cross compiling tool for clang build
        # apt-get install binutils-arm-linux-gnueabi
        # clang-22 might not be officially released. Try a lower version if installation fails.
        # https://github.com/btrfs/linux/commit/3f401162cacd05e18ed2b3beae5612a29e1e66e3
        git remote add btrfs https://github.com/btrfs/linux.git
        git fetch --no-tags btrfs inode-refcnt
        git checkout 3f401162cacd05e18ed2b3beae5612a29e1e66e3
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash fs/