Fix nightly test failure

* Both macros ARM_COMPUTE_ENABLE_FP16 and ENABLE_FP16_KERNELS
  must be declared to enable FP16

* The failure was caused by not compiling the validation suite with the same
  definitions used to compile the library. ARM_COMPUTE_ENABLE_FP16 was missing
  and the call from the test into error_on_unsupported_cpu_fp16() failed.

* Resolves COMPMID-6727

Change-Id: I278c813aef799d9d0e21e5323b2b8e9e45252d6c
Signed-off-by: Pablo Marquez Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/10848
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: SiCong Li <sicong.li@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
diff --git a/SConstruct b/SConstruct
index 746d4a6..cf8fb52 100644
--- a/SConstruct
+++ b/SConstruct
@@ -64,11 +64,11 @@
     # Manage data-types
     if env['multi_isa']:
         if  any(i in data_types for i in ['all', 'fp16']):
-            env.Append(CXXFLAGS = ['-DENABLE_FP16_KERNELS'])
+            env.Append(CXXFLAGS = ['-DENABLE_FP16_KERNELS', '-DARM_COMPUTE_ENABLE_FP16'])
     else:
             if not 'v8a' in env['arch'] and not 'v7a' in env['arch'] and not 'armv8r64' in env['arch']:
                 if  any(i in data_types for i in ['all', 'fp16']):
-                    env.Append(CXXFLAGS = ['-DENABLE_FP16_KERNELS'])
+                    env.Append(CXXFLAGS = ['-DENABLE_FP16_KERNELS','-DARM_COMPUTE_ENABLE_FP16'])
 
     if any(i in data_types for i in ['all', 'fp32']):
         env.Append(CXXFLAGS = ['-DENABLE_FP32_KERNELS'])