Only export necessary symbols

Change-Id: I869d7124c8cc555f4b09801a898f4dd3ecb072ec
diff --git a/media/ndk/Android.mk b/media/ndk/Android.mk
index 1f155f3..8f795cd 100644
--- a/media/ndk/Android.mk
+++ b/media/ndk/Android.mk
@@ -35,6 +35,8 @@
     frameworks/base/core/jni \
     frameworks/av/include/ndk
 
+LOCAL_CFLAGS += -fvisibility=hidden -D EXPORT='__attribute__ ((visibility ("default")))'
+
 LOCAL_SHARED_LIBRARIES := \
     libbinder \
     libmedia \