test: enable <misc/wbarrier_obar.lua> LuaJIT test

This patch moves the aforementioned test to the <trace/wbarrier.lua>
test, with refactoring to restore the JIT engine and GC settings after
the test.

Part of tarantool/tarantool#9398

test/LuaJIT-tests/trace/wbarrier.lua

@@ -1,3 +1,12 @@
+local function jit_opt_is_on(needed)
+  for _, opt in ipairs({jit.status()}) do
+    if opt == needed then
+      return true
+    end
+  end
+  return false
+end
+
 do --- TBAR for HSTORE.
   local t = {[0]={}}
   for i = 1, 1e5 do t[i] = {t[i - 1]} end
@@ -14,3 +23,35 @@ do --- OBAR for USTORE.
   end
   f()
 end
+
+do --- DSE of USTORE must eliminate OBAR too.
+  local need_restore_sink = false
+  if jit_opt_is_on("sink") then
+    need_restore_sink = true
+    jit.opt.start("-sink")
+  end
+
+  local f
+  do
+    local x
+    f = function()
+      local y = 0
+      for _ = 1, 10000 do
+        x = {1}
+        if y > 0 then end
+        x = 1
+      end
+    end
+  end
+
+  collectgarbage()
+  local oldstepmul = collectgarbage("setstepmul", 1)
+  collectgarbage("restart")
+
+  f()
+
+  collectgarbage("setstepmul", oldstepmul)
+  if need_restore_sink then
+    jit.opt.start("+sink")
+  end
+end