reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/Broadcom/stblinux/commit/76f20110f0216907c77d854c7f224a2b11a7ac64
        git remote add broadcom-stblinux https://github.com/Broadcom/stblinux
        git fetch --no-tags broadcom-stblinux devicetree/next
        git checkout 76f20110f0216907c77d854c7f224a2b11a7ac64
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-10.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-10.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash