Added bench/roulette.lua

This benchmark exhibits non-deterministic performance.

bench/roulette.lua

@@ -0,0 +1,20 @@
+-- Russian Roulette simulator
+-- This benchmark includes randomness from an external source that can
+-- produce non-deterministic performance.
+-- See https://github.com/LuaJIT/LuaJIT/issues/218
+
+math.randomseed(os.time())
+
+local population = 100e6
+local live = 0
+local die  = 0
+
+for i = 1, population do
+   if math.random(6) == 6 then
+      die = die + 1
+   else
+      live = live + 1
+   end
+end
+
+print(("Survived %d/%d (%.3f%%)"):format(live, population, live*100/(live+die)))