IVGCVSW-6310 Update ICustomAllocator and add GetDefaultAllocator function to backends

Signed-off-by: Francis Murtagh <francis.murtagh@arm.com>
Change-Id: If2879e8a82692285e7fa3f4d09abd608ca28de12
diff --git a/src/backends/cl/test/CMakeLists.txt b/src/backends/cl/test/CMakeLists.txt
index 41cbe24..8ee532a 100644
--- a/src/backends/cl/test/CMakeLists.txt
+++ b/src/backends/cl/test/CMakeLists.txt
@@ -17,6 +17,7 @@
     ClOptimizedNetworkTests.cpp
     ClRuntimeTests.cpp
     ClWorkloadFactoryHelper.hpp
+    DefaultAllocatorTests.cpp
     Fp16SupportTest.cpp
     OpenClTimerTest.cpp
 )