reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd.git/commit/?id=940d0dd200c80a77133156bb3e1aaed47e2a9c23
        git remote add jgg-iommufd https://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd.git
        git fetch --no-tags jgg-iommufd for-next
        git checkout 940d0dd200c80a77133156bb3e1aaed47e2a9c23
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=i386 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/iommu/iommufd/