message: use M_PI with MinGW
diff: @@ -2,7 +2,11 @@ cmake_minimum_required(VERSION 2.8.12)
  project(offboard)
  -if(MSVC OR MINGW)
  +if(MINGW)
  + add_definitions("-D_USE_MATH_DEFINES") # For M_PI
  +endif()
  +
  +if(MSVC)
  add_definitions("-std=c++11 -WX -W2")
  add_definitions("-D_USE_MATH_DEFINES") # For M_PI
  else()
  