better Grid bench build script

Grid/build-benchmark.sh

@@ -16,18 +16,16 @@ cd "${env_dir}"
 env_dir=$(pwd -P)
 cd "${call_dir}"
 build_dir="${env_dir}/build/Grid-benchmarks/${cfg}"
-if [ -d "${build_dir}" ]; then
-    echo "error: directory '${build_dir}' exists"
-    exit 1
-fi
 mkdir -p "${build_dir}"
 source "${env_dir}/env.sh"
 entry=$(jq ".configs[]|select(.name==\"${cfg}\")" "${env_dir}"/grid-config.json)
 env_script=$(echo "${entry}" | jq -r ".\"env-script\"")
 cd "${build_dir}" || return
 source "${env_dir}/${env_script}"
+if [ ! -f Makefile ]; then
     "${script_dir}/configure" --with-grid="${env_dir}/prefix/grid_${cfg}" \
                             --prefix="${env_dir}/prefix/gridbench_${cfg}"
+fi
 make -j 128
 make install
 cd "${call_dir}"