IVGCVSW-1964 : replace optional biases with home-grown Optional

!android-nn-driver:151788

Change-Id: Ibdc41d09b8df05e7a0360dcb8a060860dfb1bd99
diff --git a/Android.mk b/Android.mk
index d181054..95b10b9 100644
--- a/Android.mk
+++ b/Android.mk
@@ -193,6 +193,7 @@
 	src/armnn/test/OpenClTimerTest.cpp \
 	src/armnn/test/ProfilingEventTest.cpp \
 	src/armnn/test/ObservableTest.cpp \
+	src/armnn/test/OptionalTest.cpp \
 	src/backends/test/IsLayerSupportedTest.cpp \
 	src/backends/test/Reference.cpp \
 	src/backends/test/WorkloadDataValidation.cpp \