reproduce (this is a W=1 build):
        git remote add bcachefs https://evilpiepirate.org/git/bcachefs.git
        git fetch --no-tags bcachefs bcachefs-testing
        git checkout 4f3f9133e70fced7e1ed07a143160017a3c88e12

        # install loongarch cross compiling tool for clang build
        # apt-get install binutils-loongarch-linux-gnu
        # clang-23 might not be officially released. Try a lower version if installation fails.
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-23 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-23 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash