Add arm64-v8a build script for libx264

Signed-off-by: Leo Ma <begeekmyfriend@gmail.com>

library/src/main/libenc/jni/libx264/android_build_arm64_v8a.sh

+#!/bin/sh
+
+ANDROID_NDK=/home/leoma/MyOSP/android-ndk-r13b
+SYSROOT=$ANDROID_NDK/platforms/android-21/arch-arm64
+CROSS_PREFIX=$ANDROID_NDK/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin/aarch64-linux-android-
+EXTRA_CFLAGS="-march=armv8-a -D__ANDROID__"
+EXTRA_LDFLAGS="-nostdlib"
+PREFIX=`pwd`/libs/arm64-v8a
+
+./configure --prefix=$PREFIX \
+        --host=aarch64-linux \
+        --sysroot=$SYSROOT \
+        --cross-prefix=$CROSS_PREFIX \
+        --extra-cflags="$EXTRA_CFLAGS" \
+        --extra-ldflags="$EXTRA_LDFLAGS" \
+        --enable-pic \
+        --enable-static \
+        --enable-strip \
+        --disable-cli \
+        --disable-win32thread \
+        --disable-avs \
+        --disable-swscale \
+        --disable-lavf \
+        --disable-ffms \
+        --disable-gpac \
+        --disable-lsmash
+
+make clean
+make STRIP= -j8 install || exit 1
+
+cp -f $PREFIX/lib/libx264.a $PREFIX
+rm -rf $PREFIX/include $PREFIX/lib $PREFIX/pkgconfig