IVGCVSW-2005: Pull in backend specific unit tests into Android.mk similarly as backend sources

Change-Id: Icafc644b64c591f4dc0e1560d02b806bf053a2da
diff --git a/src/backends/common.mk b/src/backends/common.mk
index 2b649ad..b1583b9 100644
--- a/src/backends/common.mk
+++ b/src/backends/common.mk
@@ -17,3 +17,12 @@
     StringMapping.cpp \
     WorkloadData.cpp \
     WorkloadFactory.cpp
+
+# COMMON_TEST_SOURCES contains the list of files to be included
+# in the Android unit test build (armnn-tests) and it is picked
+# up by the Android.mk file in the root of ArmNN
+
+COMMON_TEST_SOURCES := \
+    test/WorkloadDataValidation.cpp \
+    test/TensorCopyUtils.cpp \
+    test/LayerTests.cpp