tests: add fchdir.test

* tests/fchdir.c: New file.
* tests/fchdir.test: New test.
* tests/.gitignore: Add fchdir.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add fchdir.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 237efa6..e33c009 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -38,6 +38,7 @@
 execveat-v
 faccessat
 fanotify_mark
+fchdir
 fchmod
 fchmodat
 fchown