linbpng 开启neon指令优化

libpng version: 1.6.1

Ref: http://mortoray.com/2012/08/21/android-ndk-cross-compile-setup-libpng-and-freetype/

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export PLATFORM_PREFIX=/tmp/opt/android-ext

# armv5

export NDK_PLATFORM=android-5

# armv7

export NDK_PLATFORM=android-8

# x86

export NDK_PLATFORM=android-9

# arm5 armv7

$NDK_ROOT/build/tools/make-standalone-toolchain.sh --platform=$NDK_PLATFORM  --install-dir=$PLATFORM_PREFIX

# x86

$NDK_ROOT/build/tools/make-standalone-toolchain.sh --platform=$NDK_PLATFORM  --install-dir=$PLATFORM_PREFIX --toolchain=x86-4.6

export PATH=$PLATFORM_PREFIX/bin:$PATH

# armv5 x86

./configure --host=arm-linux-androideabi --prefix=$PLATFORM_PREFIX

# armv7

./configure --host=arm-linux-androideabi --enable-arm-neon=on --prefix=$PLATFORM_PREFIX 

Edit arm/filter_neon.S(armv7 only): delete line 19-20, delete last line

make