Fix unused parameter warning and enable -Werror.

Test: make -j60 android.hardware.gnss@1.0-impl still compiles
Change-Id: I98256f95b77944d514971be02dc4d4b445359541
diff --git a/gnss/1.0/default/Android.mk b/gnss/1.0/default/Android.mk
index 73889b5..b4ef9a8 100644
--- a/gnss/1.0/default/Android.mk
+++ b/gnss/1.0/default/Android.mk
@@ -28,6 +28,8 @@
     android.hardware.gnss@1.0 \
     libhardware
 
+LOCAL_CFLAGS += -Werror
+
 include $(BUILD_SHARED_LIBRARY)
 
 include $(CLEAR_VARS)