etw_list - allow generated header to be included from multiple compilation units
etw_list - allow generated header to be included from multiple compilation units

Add #pragma once on top of generated header. Fixes redefinition errors and allows generated header to be included from multiple compilation units.

GameTechDev/PresentMon,GameTechDev/PresentMon,GameTechDev/PresentMon,GameTechDev/PresentMon