extensions/vp9: Control symbol visibility with libvpx.ver

This change reduces the final .so size by ~9% for armv7/arm64.

Arch : Size_before : Size_after
armeabi-v7a : 300548 : 271876
arm64-v8a : 247632 : 223056

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150648668

extensions/vp9/src/main/jni/generate_libvpx_android_configs.sh

@@ -68,7 +68,7 @@ limit=$((${#arch[@]} - 1))
 # everything else will be removed.
 allowed_files="libvpx_srcs.txt vpx_config.c vpx_config.h vpx_scale_rtcd.h"
 allowed_files+=" vp8_rtcd.h vp9_rtcd.h vpx_version.h vpx_config.asm"
-allowed_files+=" vpx_dsp_rtcd.h"
+allowed_files+=" vpx_dsp_rtcd.h libvpx.ver"
 
 remove_trailing_whitespace() {
   perl -pi -e 's/\s\+$//' "$@"

extensions/vp9/src/main/jni/libvpx.mk

@@ -54,4 +54,5 @@ LOCAL_SRC_FILES := $(sort $(LOCAL_SRC_FILES))
 LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/libvpx \
                            $(LOCAL_PATH)/libvpx/vpx
 
+LOCAL_LDFLAGS := -Wl,--version-script=$(CONFIG_DIR)/libvpx.ver
 include $(BUILD_SHARED_LIBRARY)