tests: check decoding of renameat2 syscall

* tests/renameat2.c: New file.
* tests/renameat2.test: New test.
* tests/.gitignore: Add renameat2.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add renameat2.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index c7db886..9195b5b 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -149,6 +149,7 @@
 recvmsg
 rename
 renameat
+renameat2
 restart_syscall
 rmdir
 rt_sigpending