Treat warnings as errors in VHAL unit test

Test: mm -j

Change-Id: Ic174d0550d621ef8508377db97db33f813c06ab1
Fix: b/34901911
diff --git a/automotive/vehicle/2.0/default/Android.mk b/automotive/vehicle/2.0/default/Android.mk
index 9b3323d..4a010e9 100644
--- a/automotive/vehicle/2.0/default/Android.mk
+++ b/automotive/vehicle/2.0/default/Android.mk
@@ -133,7 +133,7 @@
     libutils \
     $(vhal_v2_0) \
 
-LOCAL_CFLAGS += -Wall -Wextra
+LOCAL_CFLAGS += -Wall -Wextra -Werror
 LOCAL_MODULE_TAGS := tests
 
 include $(BUILD_NATIVE_TEST)