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/GEMMLowp.cpp b/tests/validation/reference/GEMMLowp.cpp
index 36d86d1..85a98e4 100644
--- a/tests/validation/reference/GEMMLowp.cpp
+++ b/tests/validation/reference/GEMMLowp.cpp
@@ -69,6 +69,9 @@
     const int  cols_in        = in->shape().x();
     const bool is_per_channel = result_mult_int.size() > 1;
 
+#if defined(_OPENMP)
+    #pragma omp parallel for
+#endif /* _OPENMP */
     for(int i = 0; i < in->num_elements(); ++i)
     {
         int32_t result = ((*in)[i] + result_offset);
@@ -100,6 +103,9 @@
     const int  cols_in        = in->shape().x();
     const bool is_per_channel = result_fixedpoint_multiplier.size() > 1;
 
+#if defined(_OPENMP)
+    #pragma omp parallel for
+#endif /* _OPENMP */
     for(int i = 0; i < in->num_elements(); ++i)
     {
         TIn result = (*in)[i];
@@ -141,6 +147,9 @@
     const int  cols_in        = in->shape().x();
     const bool is_per_channel = result_real_multiplier.size() > 1;
 
+#if defined(_OPENMP)
+    #pragma omp parallel for
+#endif /* _OPENMP */
     for(int i = 0; i < in->num_elements(); ++i)
     {
         TIn result = (*in)[i];