tests/bench: Add variation on loop_count/while_down_ne test.

tests/bench/loop_count-5.1-while_down_ne_localvar.py

@@ -0,0 +1,8 @@
+import bench
+
+def test(num):
+    zero = 0
+    while num != zero:
+        num -= 1
+
+bench.run(test)