message: Check availability of accept4 in C++ instad of C code.
diff: @@ -9,7 +9,7 @@ set(CMAKE_REQUIRED_DEFINITIONS -D_GNU_SOURCE)
  check_symbol_exists(ppoll poll.h HAVE_PPOLL)
  set(CMAKE_REQUIRED_DEFINITIONS)
  check_symbol_exists(sigaction signal.h HAVE_SIGACTION)
  -check_symbol_exists(accept4 "sys/socket.h" HAVE_ACCEPT4)
  +check_cxx_symbol_exists(accept4 "sys/socket.h" HAVE_ACCEPT4)
  check_include_file(termios.h HAVE_TERMIOS_H)
  check_include_files("sys/types.h;sys/event.h" HAVE_SYS_EVENT_H)
  