set: add cstddef for offsetof macro

src/core/hle/service/set/appln_settings.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <array>
+#include <cstddef>
 
 #include "common/common_types.h"
 

src/core/hle/service/set/device_settings.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <array>
+#include <cstddef>
 
 #include "common/common_types.h"