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/ComputeAllAnchors.cpp b/tests/validation/reference/ComputeAllAnchors.cpp
index 60be7ef..9654da2 100644
--- a/tests/validation/reference/ComputeAllAnchors.cpp
+++ b/tests/validation/reference/ComputeAllAnchors.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019 ARM Limited.
+ * Copyright (c) 2019-2020 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -49,6 +49,9 @@
     T              *all_anchors_ptr = all_anchors.data();
 
     // Iterate over the input grid and anchors
+#if defined(_OPENMP)
+    #pragma omp parallel for schedule(dynamic, 1) collapse(3)
+#endif /* _OPENMP */
     for(int y = 0; y < height; y++)
     {
         for(int x = 0; x < width; x++)