tests: add a test for get_robust_list and set_robust_list decoding

* tests/xet_robust_list.c: New file.
* tests/xet_robust_list.test: New test.
* tests/Makefile.am (check_PROGRAMS): Add xet_robust_list.
(TESTS): Add xet_robust_list.test.
* tests/.gitignore: Add xet_robust_list.
diff --git a/tests/.gitignore b/tests/.gitignore
index f709d7f..9cf3d9b 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -49,6 +49,7 @@
 unix-pair-send-recv
 utime
 xattr
+xet_robust_list
 *.log
 *.log.*
 *.o