message: [style] set c standard to c99
diff: @@ -36,6 +36,11 @@ option(OTBR_UNSECURE_JOIN "Enable unsecure joining" OFF)
  option(OTBR_WEB "Build Web GUI" OFF)
  +if(NOT CMAKE_C_STANDARD)
  + set(CMAKE_C_STANDARD 99)
  + set(CMAKE_C_STANDARD_REQUIRED ON)
  +endif()
  +
  if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 11)
  set(CMAKE_CXX_STANDARD_REQUIRED ON)
  