cpp: don't exit with an error count, or we'll overflow to 0 and 'succeed'

*** 1065,1075 ****
  
          va_start(args, fmt);
          verror(fmt, args);
          va_end(args);
  
!         ++exfail;
  }
  
  /* VARARGS1 */
  void
  yyerror(char *fmt, ...)
--- 1065,1075 ----
  
          va_start(args, fmt);
          verror(fmt, args);
          va_end(args);
  
!         exfail = 1;
  }
  
  /* VARARGS1 */
  void
  yyerror(char *fmt, ...)
*** 1085,1095 ****
  static void
  ppwarn(char *fmt, ...)
  {
          va_list args;
          int fail = exfail;
-         exfail = -1;
  
          va_start(args, fmt);
          verror(fmt, args);
          va_end(args);
  
--- 1085,1094 ----