Add benchmark tasks combined from systemc/pc_sfifo and systemc/token_ring

Used in 'Dirk Beyer, Marie-Christine Jakobs, Thomas Lemberger: Difference Verification with Conditions, SEFM20'

Author: lembergerth

c/check.py

@@ -119,6 +119,7 @@
     ("eca-rers2018", "unexpected file RERS_18_solutions_dot_petri.csv"),
     ("eca-rers2018", "unexpected file createYml.py"),
     ("nla-digbench-scaling", "unexpected file generate.py"),
+    ("combinations", "unexpected file generate-tasks.py"),
 
     # historical
     ("ntdrivers", "missing readme"),