message: Fix windows build broken in r316915
  I accidentally left a linux-specific include in generic code.
diff: #include <csignal>
  #include <time.h>
  #include <vector>
  -#include <sys/syscall.h>
  // Multiplexing is implemented using kqueue on systems that support it (BSD
  // variants including OSX). On linux we use ppoll, while android uses pselect
  