reproduce (this is a W=1 build):
        # https://github.com/koverstreet/bcachefs/commit/931ffb231a45d53ede3ea0e28f28de35c7817a55
        git remote add koverstreet-bcachefs https://github.com/koverstreet/bcachefs
        git fetch --no-tags koverstreet-bcachefs bcachefs-testing
        git checkout 931ffb231a45d53ede3ea0e28f28de35c7817a55
        # 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 fs/