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/GEMM.cpp b/tests/validation/reference/GEMM.cpp
index 3c72b94..20def87 100644
--- a/tests/validation/reference/GEMM.cpp
+++ b/tests/validation/reference/GEMM.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019 ARM Limited.
+ * Copyright (c) 2017-2020 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -23,6 +23,7 @@
  */
 #include "GEMM.h"
 
+#include "arm_compute/core/Helpers.h"
 #include "arm_compute/core/Types.h"
 
 namespace arm_compute
@@ -55,6 +56,9 @@
     const int c_stride_z = N * M;
     const int c_stride_w = N * M * D;
 
+#if defined(_OPENMP)
+    #pragma omp parallel for collapse(2)
+#endif /* _OPENMP */
     for(int w = 0; w < W; ++w)
     {
         for(int depth = 0; depth < D; ++depth)
@@ -107,6 +111,9 @@
     const int c_stride_z = N * M;
     const int c_stride_w = N * M * D;
 
+#if defined(_OPENMP)
+    #pragma omp parallel for collapse(2)
+#endif /* _OPENMP */
     for(int w = 0; w < W; ++w)
     {
         for(int depth = 0; depth < D; ++depth)