reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-47-g365b9520-dirty
        git remote add bcachefs https://evilpiepirate.org/git/bcachefs.git
        git fetch --no-tags bcachefs bcachefs-testing
        git checkout 66ac54850bf4b835b7c2d96c1e23bce582c437bf
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=i386 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=i386 SHELL=/bin/bash fs/bcachefs/