tests: add fchmodat.test

* tests/fchmodat.c: New file.
* tests/fchmodat.test: New test.
* tests/.gitignore: Add fchmodat.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add fchmodat.test.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index c8f6fa1..ba5b301 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -85,6 +85,7 @@
 	faccessat \
 	fanotify_mark \
 	fchmod \
+	fchmodat \
 	fcntl \
 	fcntl64 \
 	fdatasync \
@@ -275,6 +276,7 @@
 	faccessat.test \
 	fanotify_mark.test \
 	fchmod.test \
+	fchmodat.test \
 	fcntl.test \
 	fcntl64.test \
 	fdatasync.test \