Add error for format and make sure setActiveConfig fails with an invalid mode.

Change-Id: Iacdb5cbad125787f96c64c88d432fc541c4cad1a
diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index f279491..183478d 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -83,7 +83,7 @@
     LOCAL_CFLAGS += -DPRESENT_TIME_OFFSET_FROM_VSYNC_NS=0
 endif
 
-LOCAL_CFLAGS += -fvisibility=hidden
+LOCAL_CFLAGS += -fvisibility=hidden -Werror=format
 LOCAL_CFLAGS += -std=c++11
 
 LOCAL_SHARED_LIBRARIES := \