add openmp, test=develop

lite/backends/arm/math/pooling.cc

@@ -86,6 +86,7 @@ void pooling_basic(const float* din,
     }
   } else {
     for (int ind_n = 0; ind_n < num; ++ind_n) {
+#pragma omp parallel for
       for (int ind_c = 0; ind_c < chin; ++ind_c) {
         for (int ind_h = 0; ind_h < hout; ++ind_h) {
           int sh = ind_h * stride_h;