message: Update single_pass_tests/loop to check output value.
diff: (module
  - (func $main (export "main") (result i32)
  + (func $main (export "main")
  (local $count i32)
  (local $sum i32)
  (loop (result i32)
  (set_local $sum (i32.add (get_local $sum) (get_local $count)))
  (i32.sub (i32.const 1) (i32.eq
  (get_local $count)
  - (i32.const 100000)
  + (i32.const 50000)
  ))
  (br_if 0)
  (get_local $sum)
  )
  + (if (i32.ne (i32.const 1250025000)) (unreachable))
  )
  )
  