Donot Preprocessing for libpng
不要预处理libpng

Signed-off-by: Wanpeng Song <swpustc@mail.ustc.edu.cn>
Merge branch 'sources' into projects

Signed-off-by: Wanpeng Song <swpustc@mail.ustc.edu.cn>
Processing...
预处理...

Signed-off-by: Wanpeng Song <swpustc@mail.ustc.edu.cn>