reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?id=168c8d86d8ac87a04878717d8d13d6b63339db8d
        git remote add brauner-vfs https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
        git fetch --no-tags brauner-vfs work.procfs
        git checkout 168c8d86d8ac87a04878717d8d13d6b63339db8d
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash