Add some basic debug output for log compression

Guarded by --debug=compress, like the other debug measures.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/debug.h b/debug.h
index e248695..923fa39 100644
--- a/debug.h
+++ b/debug.h
@@ -20,6 +20,7 @@
 	FD_TIME,
 	FD_NET,
 	FD_RATE,
+	FD_COMPRESS,
 	FD_DEBUG_MAX,
 };