message: [lldb] [MainLoop] Report errno for failed kevent()
  Modify the kevent() error reporting to use errno rather than returning
  the return value.  At least on FreeBSD and NetBSD, kevent() always
  returns -1 in case of error, and the actual error is returned via errno.
diff: @@ -108,7 +108,7 @@ Status MainLoop::RunImpl::Poll() {
  out_events, llvm::array_lengthof(out_events), nullptr);
  if (num_events < 0)
  - return Status("kevent() failed with error %d\n", num_events);
  + return Status(errno, eErrorTypePOSIX);
  return Status();
  }
  