2976 remove useless offsetof() macros

@@ -26,10 +26,11 @@
 
 #ifndef _SYS_ECPPVAR_H
 #define _SYS_ECPPVAR_H
 
 #include <sys/note.h>
+#include <sys/sysmacros.h>
 
 #ifdef  __cplusplus
 extern "C" {
 #endif
 

@@ -511,11 +512,10 @@
 
 /*
  * Other useful macros
  */
 #define NELEM(a)        (sizeof (a) / sizeof (*(a)))
-#define offsetof(s, m)  ((size_t)(&(((s *)0)->m)))
 
 #ifdef  __cplusplus
 }
 #endif