Turn on -Wunused and fix the mistakes it uncovers.

Change-Id: I023d2d8b547fbc21d4124bb7510d42b06a0dc501
diff --git a/libc/Android.mk b/libc/Android.mk
index 4783bd3..02fad3b 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -486,7 +486,7 @@
 # ========================================================
 libc_common_cflags := \
     -D_LIBC=1 \
-    -Wall -Wextra \
+    -Wall -Wextra -Wunused \
 
 # Try to catch typical 32-bit assumptions that break with 64-bit pointers.
 libc_common_cflags += \
@@ -709,7 +709,7 @@
 LOCAL_SRC_FILES := $(libc_upstream_openbsd_src_files)
 LOCAL_CFLAGS := \
     $(libc_common_cflags) \
-    -Wno-sign-compare -Wno-uninitialized \
+    -Wno-sign-compare -Wno-uninitialized -Wno-unused-parameter \
     -Werror \
     -I$(LOCAL_PATH)/upstream-openbsd/android/include \
     -I$(LOCAL_PATH)/upstream-openbsd/lib/libc/include \