reproduce (this is a W=1 build):
        # https://github.com/awilliam/linux-vfio/commit/a975fd177726e110f30b561dd0707b78f21ffe66
        git remote add awilliam-vfio https://github.com/awilliam/linux-vfio.git
        git fetch --no-tags awilliam-vfio for-linus
        git checkout a975fd177726e110f30b561dd0707b78f21ffe66

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

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