reproduce (this is a W=1 build):
        # https://github.com/gourryinverse/linux/commit/9fb117618cd8a8687bae14185d28b33360452bd9
        git remote add gourryinverse https://github.com/gourryinverse/linux
        git fetch --no-tags gourryinverse scratch/gourry/cxl/compression/file_cleancache
        git checkout 9fb117618cd8a8687bae14185d28b33360452bd9
        # apt-get install sparse
        # sparse: v0.6.5-rc1

        # 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=x86_64 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 SHELL=/bin/bash mm/