2976 remove useless offsetof() macros

*** 26,35 ****
--- 26,36 ----
  
  #ifndef _SYS_ECPPVAR_H
  #define _SYS_ECPPVAR_H
  
  #include <sys/note.h>
+ #include <sys/sysmacros.h>
  
  #ifdef  __cplusplus
  extern "C" {
  #endif
  
*** 511,521 ****
  
  /*
   * Other useful macros
   */
  #define NELEM(a)        (sizeof (a) / sizeof (*(a)))
- #define offsetof(s, m)  ((size_t)(&(((s *)0)->m)))
  
  #ifdef  __cplusplus
  }
  #endif
  
--- 512,521 ----