COMPMID-3314: Enable OpenMP in the reference tests

Change-Id: I05b5fedb998317144e0dd13a6377a97207b27f46
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/3024
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/validation/reference/ArithmeticOperations.cpp b/tests/validation/reference/ArithmeticOperations.cpp
index d86833f..fd32f45 100644
--- a/tests/validation/reference/ArithmeticOperations.cpp
+++ b/tests/validation/reference/ArithmeticOperations.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019 ARM Limited.
+ * Copyright (c) 2017-2020 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -62,13 +62,16 @@
         id_src1.set(dim - 1, 0);
         id_src2.set(dim - 1, 0);
         id_dst.set(dim - 1, 0);
-
-        for(size_t i = 0; i < dst.shape()[dim - 1]; ++i, ++id_dst[dim - 1])
+#if defined(_OPENMP)
+        #pragma omp parallel for
+#endif /* _OPENMP */
+        for(size_t i = 0; i < dst.shape()[dim - 1]; ++i)
         {
             BroadcastUnroll < dim - 1 >::unroll(op, src1, src2, dst, convert_policy, id_src1, id_src2, id_dst);
 
             id_src1[dim - 1] += !src1_is_broadcast;
             id_src2[dim - 1] += !src2_is_broadcast;
+            ++id_dst[dim - 1];
         }
     }
 };