Turn on -Wunused and fix the mistakes it uncovers.

Change-Id: I023d2d8b547fbc21d4124bb7510d42b06a0dc501
diff --git a/libdl/Android.mk b/libdl/Android.mk
index 3d60474..cb1cb7d 100644
--- a/libdl/Android.mk
+++ b/libdl/Android.mk
@@ -22,7 +22,7 @@
 LOCAL_LDFLAGS_x86_64 := $(LOCAL_LDFLAGS_x86)
 
 LOCAL_SRC_FILES:= libdl.c
-LOCAL_CFLAGS := -Wall -Wextra -Werror
+LOCAL_CFLAGS := -Wall -Wextra -Wunused -Werror
 
 LOCAL_MODULE := libdl
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk