Turn on -Wunused and fix the mistakes it uncovers.

Change-Id: I023d2d8b547fbc21d4124bb7510d42b06a0dc501
diff --git a/linker/Android.mk b/linker/Android.mk
index d2bcfaf..811cf6e 100644
--- a/linker/Android.mk
+++ b/linker/Android.mk
@@ -26,7 +26,7 @@
     -fno-stack-protector \
     -Wstrict-overflow=5 \
     -fvisibility=hidden \
-    -Wall -Wextra -Werror \
+    -Wall -Wextra -Wunused -Werror \
 
 LOCAL_CONLYFLAGS += \
     -std=gnu99 \