message: build_system: set c++11 standard with the CMake property
diff: @@ -4,12 +4,13 @@ set(CMAKE_INSTALL_PREFIX "../install" CACHE PATH "default cache path")
  project(dronecore)
  +set_property(GLOBAL PROPERTY CXX_STANDARD 11)
  +
  if(NOT MSVC)
  # Clang and GCC
  # We want C++11 and lots of warnings.
  # We are not using exceptions to make it easier to write wrappers.
  add_definitions(
  - -std=c++11
  -fno-exceptions
  )
  @@ -32,7 +33,6 @@ if(NOT MSVC)
  else()
  # MSBuild
  add_definitions(
  - -std=c++11
  -DWINDOWS
  )
  