5042 stop using deprecated atomic functions

*** 165,175 ****
                  do {
                          old = panicbuf_index;
                          new = old + len;
                          if (new >= PANICBUFSIZE)
                                  new = panicbuf_log + len;
!                 } while (cas32(&panicbuf_index, old, new) != old);
                  bcopy(body, &panicbuf[new - len], len);
          }
          if (bufp != buf)
                  kmem_free(bufp, bufsize);
  }
--- 165,175 ----
                  do {
                          old = panicbuf_index;
                          new = old + len;
                          if (new >= PANICBUFSIZE)
                                  new = panicbuf_log + len;
!                 } while (atomic_cas_32(&panicbuf_index, old, new) != old);
                  bcopy(body, &panicbuf[new - len], len);
          }
          if (bufp != buf)
                  kmem_free(bufp, bufsize);
  }