IVGCVSW-4368 Update Android.mk and backend.mk files with latest unit tests

* Sync up the Android build files with the CMakeLists.txt

Signed-off-by: Colm Donelan <Colm.Donelan@arm.com>
Change-Id: I1675b0937fed7c74833e46af6d077ced57cf5bed
diff --git a/src/backends/reference/backend.mk b/src/backends/reference/backend.mk
index 412dc94..1987bd5 100644
--- a/src/backends/reference/backend.mk
+++ b/src/backends/reference/backend.mk
@@ -115,6 +115,7 @@
 # Include the source files for the CL backend tests
 
 BACKEND_TEST_SOURCES := \
+        test/ArgMinMaxTests.cpp \
         test/RefCreateWorkloadTests.cpp \
         test/RefDetectionPostProcessTests.cpp \
         test/RefEndToEndTests.cpp \
@@ -123,7 +124,8 @@
         test/RefLayerTests.cpp \
         test/RefMemoryManagerTests.cpp \
         test/RefOptimizedNetworkTests.cpp \
-        test/RefRuntimeTests.cpp
+        test/RefRuntimeTests.cpp \
+        test/RefTensorHandleTests.cpp
 else
 
 # ARMNN_REF_ENABLED == 0