cpio: Turn on -Werror

- Solve st_mode is uint16_t on MAC
- Turn on -Werror

Change-Id: I67b62424245545099ed283c56dae544153b85425
diff --git a/cpio/Android.mk b/cpio/Android.mk
index 5184463..575beb2 100644
--- a/cpio/Android.mk
+++ b/cpio/Android.mk
@@ -8,6 +8,8 @@
 
 LOCAL_MODULE := mkbootfs
 
+LOCAL_CFLAGS := -Werror
+
 include $(BUILD_HOST_EXECUTABLE)
 
 $(call dist-for-goals,dist_files,$(LOCAL_BUILT_MODULE))