Fix baremetal arm_compute_validation build errors

* Add -C flag to instruct preprocessor not to strip comments. This is to
prevent marker comments like '// fall through' that suppresses certain
warnings from being removed.

* Fix unused variable warnings.

* Add M_PI definition that's missing from certain toolchain standard
libraries.

Resolves COMPMID-4054

Change-Id: I1d641db668685d4b678f3d0efed84bfe9e630b4b
Signed-off-by: SiCongLi <sicong.li@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4692
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/core/NEON/kernels/NEFFTRadixStageKernel.cpp b/src/core/NEON/kernels/NEFFTRadixStageKernel.cpp
index cb1391a..971d4fd 100644
--- a/src/core/NEON/kernels/NEFFTRadixStageKernel.cpp
+++ b/src/core/NEON/kernels/NEFFTRadixStageKernel.cpp
@@ -32,6 +32,7 @@
 #include "src/core/NEON/wrapper/wrapper.h"
 #include "src/core/helpers/AutoConfiguration.h"
 #include "src/core/helpers/WindowHelpers.h"
+#include "support/ToolchainSupport.h"
 
 #include <arm_neon.h>
 #include <cmath>