Rime now set alsologtostderr by default in SetupLogging, but still there's no way to log only to stderr.

I feel it's redundant, at least from fcitx dev pov, to write log to both stderr and log file.

While it's possible to omit app name to skip glog setup, then the min log level will be ignored.

I suggest if log dir is null, set logtostderr=1 to make it only log to stderr.

Or, if you want to keep backward compatibility on the API, define a new way to enforce log only to stderr (e.g. when log_dir is empty "").