Cmake : Build directory in include path

I'm looking for the good way to add the build directory (which is different from my source directory, a git repository) to the include path for gcc, in order to have the classic "config.h" file for portability seen during the compilation.

From stackoverflow

• Are you looking for this -I$(DIR)?

  claferri : No I found myself what I was looking for, it was a cmake variable. Thx anyway +1.

• I was looking for

  include_directories (${CMAKE_BINARY_DIR})
  

  To add the build directory in case of out-of-source build.