Improve ETA for fill_device based job files

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/os/os.h b/os/os.h
index b7fce80..218766a 100644
--- a/os/os.h
+++ b/os/os.h
@@ -147,4 +147,11 @@
 }
 #endif
 
+#ifndef FIO_HAVE_FS_STAT
+static inline unsigned long long get_fs_size(const char *path)
+{
+	return 0;
+}
+#endif
+
 #endif