Pass arch/os in probe

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/os/os-mac.h b/os/os-mac.h
index 24e0eb5..80c49f4 100644
--- a/os/os-mac.h
+++ b/os/os-mac.h
@@ -1,6 +1,8 @@
 #ifndef FIO_OS_APPLE_H
 #define FIO_OS_APPLE_H
 
+#define	FIO_OS	os_mac
+
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/disk.h>