android-nn-driver: disable unused warnings

service.cpp triggers a variety of warnings about unused code.  This
source file is used for different versions of the HAL so this is
expected, so this patch disables the warnings.

Test: local build
Change-Id: Ib11ddfe67b7e79ca1a82c2810a4f5f02c71186ef
diff --git a/Android.mk b/Android.mk
index ebd14cd..01e4fae 100644
--- a/Android.mk
+++ b/Android.mk
@@ -598,7 +598,11 @@
         -std=$(CPP_VERSION) \
         -fexceptions \
         -DARMNN_ANDROID_NN_V1_2 \
-        -DBOOST_NO_AUTO_PTR
+        -DBOOST_NO_AUTO_PTR \
+        -Wno-unused-variable \
+        -Wno-unneeded-internal-declaration \
+        -Wno-unused-function \
+        -Wno-unused-local-typedef
 
 ifeq ($(ARMNN_DRIVER_DEBUG),1)
 LOCAL_CFLAGS += \