Add two more small tests

bootstraptest/test_yjit_new_backend.rb

@@ -134,3 +134,41 @@ def foo(n)
     end
     foo(3)
 }
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+# Microbenchmark with a loop, opt_lt
+assert_equal '55', %q{
+    def foo(n)
+        i = 0
+        s = 0
+        while i < n do
+            i += 1
+            s += i
+        end
+        s
+    end
+    foo(10)
+}
+
+# Small recursive microbenchmark
+assert_equal '21', %q{
+    def fib(n)
+        if n < 2
+            return n
+        end
+        return fib(n-1) + fib(n-2)
+    end
+    fib(8)
+}