offsetof is actually a standard thing nowadays it would seem

Engine/source/console/consoleTypes.h

@@ -48,11 +48,7 @@
 /// @{
 
 #ifndef Offset
-#if defined(TORQUE_COMPILER_GCC) && (__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 1))
-#define Offset(m,T) ((int)(&((T *)1)->m) - 1)
-#else
-#define Offset(x, cls) ((dsize_t)((const char *)&(((cls *)0)->x)-(const char *)0))
-#endif
+#define Offset(x, cls) offsetof(cls, x)
 #endif
 
 class GFXShader;