tests: check decoding of futimesat syscall

* tests/futimesat.c: New file.
* tests/futimesat.test: New test.
* tests/.gitignore: Add futimesat.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add futimesat.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 4eb3f49..bcbf695 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -61,6 +61,7 @@
 fsync
 ftruncate
 ftruncate64
+futimesat
 getcwd
 getdents
 getdents64