Synergy C11 stdio.h is missing sscanf_s

I would like to use the safer version of sscanf() that is defined in C11 as sscanf_s().

In my Synergy project is e2 studio, I have tried both the GNU C11 and the ISO C11 in my project setting, but sscanf_s() is not defined.

Can somebody explain why sscanf_s() is not defined?

Thanks,

Bruce