Fix compiler error in the validation tests

* Building with openmp=1 cppthreads=0 caused a linker error in the
  validation suite

Change-Id: I16d8a49e9190cd1288237d82583a0034e20a9f38
Signed-off-by: Pablo Marquez Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/11483
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Gunes Bayir <gunes.bayir@arm.com>
Reviewed-by: Jakub Sujak <jakub.sujak@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/validation/UNIT/CPPScheduler.cpp b/tests/validation/UNIT/CPPScheduler.cpp
index 5243165..6a3f681 100644
--- a/tests/validation/UNIT/CPPScheduler.cpp
+++ b/tests/validation/UNIT/CPPScheduler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Arm Limited.
+ * Copyright (c) 2023-2024 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -68,8 +68,7 @@
 
 TEST_SUITE(UNIT)
 TEST_SUITE(CPPScheduler)
-
-#if !defined(BARE_METAL)
+#if defined(ARM_COMPUTE_CPP_SCHEDULER) && !defined(BARE_METAL)
 TEST_CASE(RethrowException, framework::DatasetMode::ALL)
 {
     CPPScheduler scheduler;
@@ -87,7 +86,6 @@
     }
     ARM_COMPUTE_EXPECT_FAIL("Expected exception not caught", framework::LogLevel::ERRORS);
 }
-#endif // !defined(BARE_METAL)
-
+#endif // defined(ARM_COMPUTE_CPP_SCHEDULER) &&  !defined(BARE_METAL)
 TEST_SUITE_END()
 TEST_SUITE_END()