reproduce (this is a W=1 build):
        # https://github.com/ceph/ceph-client/commit/88d679bc66688124f73a2e30617c12a14bb5aeff
        git remote add ceph-client https://github.com/ceph/ceph-client.git
        git fetch --no-tags ceph-client testing
        git checkout 88d679bc66688124f73a2e30617c12a14bb5aeff

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # apt-get install sparse
        # sparse: v0.6.5-rc1-21-g84ec0658

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=m68k olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=m68k SHELL=/bin/bash fs/ceph/