Add missing include <stdarg.h>
Add missing include <stdarg.h>

Summary: Zygfryd complains about undefined references.

Test Plan: none

Reviewers: kfyatek, mkrawiec

Reviewed By: kfyatek, mkrawiec

Differential Revision: https://phabricator.avsystem.com/D5127

AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons