Fix build/compile for non-blktrace platforms

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 9a43c6f..2104e3a 100644
--- a/fio.h
+++ b/fio.h
@@ -826,8 +826,10 @@
 /*
  * blktrace support
  */
+#ifdef FIO_HAVE_BLKTRACE
 extern int is_blktrace(const char *);
 extern int load_blktrace(struct thread_data *, const char *);
+#endif
 
 /*
  * If logging output to a file, stderr should go to both stderr and f_err