Provide the option to enable debug information during tar backups

Change-Id: Ibdb060d334c8f799a283f1bcef4a369d5555c975
diff --git a/libtar/block.c b/libtar/block.c
index 8116736..6285547 100755
--- a/libtar/block.c
+++ b/libtar/block.c
@@ -18,6 +18,10 @@
 # include <stdlib.h>
 #endif
 
+#ifdef TW_LIBTAR_DEBUG
+#define DEBUG 1
+#endif
+
 #ifdef HAVE_EXT4_CRYPT
 #include "ext4crypt_tar.h"
 #endif