message: Change the way C++11 standard is specified for the project.
  The old way (via target_compile_features) is dropping -std=c++11 if CMake
  decides (errorneously) is a baseline. This causes miscompilation, and
  specifically an error in Appveyor build caused by macro definition of
  "linux" variable.
diff: @@ -294,7 +294,11 @@ else()
  set_source_files_properties(${BISON_OUTPUT} PROPERTIES COMPILE_FLAGS "/wd4005 /wd4065")
  endif()
  -target_compile_features(${PROJECT_NAME} PRIVATE cxx_std_11)
  +# Set C++ standard to C++11.
  +set_target_properties(${PROJECT_NAME} PROPERTIES
  + CXX_STANDARD 11
  + CXX_STANDARD_REQUIRED YES)
  +
  if (UNIX)
  set_target_properties(${PROJECT_NAME} PROPERTIES CXX_EXTENSIONS OFF)
  target_compile_options(${PROJECT_NAME} PRIVATE -Wno-c99-extensions -Wno-deprecated-register -fno-rtti)
  