message: cmake: add define for APPLE
diff: @@ -29,6 +29,11 @@ else()
  set(curl_lib ${WIN_CURL_LIB})
  endif()
  +# We need a define if on APPLE
  +if(APPLE)
  + add_definitions("-DAPPLE")
  +endif()
  +
  # Clang needs this warning disabled.
  if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_definitions("-stdlib=libc++ -Wno-missing-braces")
  