Enable strict warnings and fix unused warnings

Test: builds without warnings
Change-Id: I0701a44cbd9a2adc405a1e253b57df7ee03a90b7
diff --git a/media/libeffects/visualizer/Android.mk b/media/libeffects/visualizer/Android.mk
index c92c543..ddcc565 100644
--- a/media/libeffects/visualizer/Android.mk
+++ b/media/libeffects/visualizer/Android.mk
@@ -7,6 +7,7 @@
 	EffectVisualizer.cpp
 
 LOCAL_CFLAGS+= -O2 -fvisibility=hidden
+LOCAL_CFLAGS += -Wall -Werror
 
 LOCAL_SHARED_LIBRARIES := \
 	libcutils \