reproduce (this is a W=1 build):
        # https://github.com/davidhildenbrand/linux/commit/21143629e50fc0929fea624f4bf416dbd35541ef
        git remote add davidhildenbrand https://github.com/davidhildenbrand/linux
        git fetch --no-tags davidhildenbrand b4/bootmem_info
        git checkout 21143629e50fc0929fea624f4bf416dbd35541ef

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/