Use non-ARC files into an ARC project

Some time we need to use some old non-ARC files/libraries into our ARC projects on iOS. We can do this in 2 ways:

1.- the first obvious way is just refactor the code to accomplish the ARC rules
2.- the easier way is de following:
- Select your project target
- Go to "Build Phases"
- Select "Compile Sources"
- On each file you want to avoid using ARC add the compiler
flag: -fno-objc-arc