tests: add sched_yield.test

* tests/sched_yield.c: New file.
* tests/sched_yield.test: New test.
* tests/.gitignore: Add sched_yield.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add sched_yield.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 4d1d8cb..4eb3f49 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -162,6 +162,7 @@
 sched_xetattr
 sched_xetparam
 sched_xetscheduler
+sched_yield
 scm_rights
 seccomp-filter
 seccomp-filter-v