remove memory leak from run-pass test

tests/run-pass/option_box_transmute_ptr.rs

@@ -3,7 +3,10 @@ fn option_box_deref() -> i32 {
     let val = Some(Box::new(42));
     unsafe {
         let ptr: *const i32 = std::mem::transmute::<Option<Box<i32>>, *const i32>(val);
-        *ptr
+        let ret = *ptr;
+        // unleak memory
+        std::mem::transmute::<*const i32, Option<Box<i32>>>(ptr);
+        ret
     }
 }