tests: check decoding of prlimit64 syscall

* tests/prlimit64.c: New file.
* tests/prlimit64.test: New test.
* tests/.gitignore: Add prlimit64.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add prlimit64.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 8f4d6f0..e20bb77 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -165,6 +165,7 @@
 preadv
 preadv-pwritev
 preadv2-pwritev2
+prlimit64
 pselect6
 ptrace
 pwritev