IVGCVSW-3656 Make the reference backend optional

 * Made the build of the reference backend depend on a new ARMCOMPUTEREF
   macro
 * Made the relevant targets dependent on the ref backend
 * Moved Cl and Neon static registry initializers to separate files
 * Wrapped some of the unit tests into proper ifdefs where necessary

Change-Id: I7f2c42699682630233a4c4b6aed2f005083de189
Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>
diff --git a/src/backends/neon/NeonRegistryInitializer.cpp b/src/backends/neon/NeonRegistryInitializer.cpp
new file mode 100644
index 0000000..c74acae
--- /dev/null
+++ b/src/backends/neon/NeonRegistryInitializer.cpp
@@ -0,0 +1,25 @@
+//
+// Copyright © 2017 Arm Ltd. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#include "NeonBackend.hpp"
+
+#include <backendsCommon/BackendRegistry.hpp>
+
+namespace
+{
+
+using namespace armnn;
+
+static BackendRegistry::StaticRegistryInitializer g_RegisterHelper
+{
+    BackendRegistryInstance(),
+    NeonBackend::GetIdStatic(),
+    []()
+    {
+        return IBackendInternalUniquePtr(new NeonBackend);
+    }
+};
+
+} // Anonymous namespace