Incompatible truncate behavior for long binary literal with `BIT_COUNT`

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```sql
select BIT_COUNT(b'1010010001000010000010000001000000010000000010000000001000000000010000000000010000000000001');
```

### 2. What did you expect to see? (Required)

MySQL's result is `0` with truncate warning thrown.

### 3. What did you see instead (Required)

TiDB's result is `64` with truncate warning thrown.

### 4. What is your TiDB version? (Required)

current master