message: Fix build on VS2019
diff: #include "os/os_specific.h"
  #include "strings/string_utils.h"
  +#include <string>
  +
  typedef int(WSAAPI *PFN_WSASTARTUP)(__in WORD wVersionRequested, __out LPWSADATA lpWSAData);
  typedef int(WSAAPI *PFN_WSACLEANUP)();
  