title: CMake compile options for libpng
body: <p>I am using libpng in my project. Right now, I can compile my project with: g++ *.cpp `libpng-config --ldflags` </p>
  
  <p>I want to switch to using CMake for easy recompiling but I don't know what to do for the libpng part. How do I provide `libpng-config --ldflags` with CMake?</p>