Disable Vsync while holding tab to disable the frame limit, and allow toggling vsync while emulation is running in OGL.

D3D9 still doesn't support changing vsync while emulation is running.

Fixes issue 6111.

Source/Core/VideoCommon/Src/VideoConfig.h

@@ -67,6 +67,7 @@ struct VideoConfig
 	void Save(const char *ini_file);
 	void GameIniSave(const char* default_ini, const char* game_ini);
 	void UpdateProjectionHack();
+	bool IsVSync();
 
 	// General
 	bool bVSync;