tests: check decoding of fchown32 syscall

* tests/fchown32.c: New file.
* tests/fchown32.test: New test.
* tests/.gitignore: Add fchown32.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add fchown32.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 5bb8b59..f3ee629 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -41,6 +41,7 @@
 fchmod
 fchmodat
 fchown
+fchown32
 fchownat
 fcntl
 fcntl64