[Compile] Some compile warning in gcc > 8

**Describe the bug**
clearing an object of type 'struct ' with no trivial copy-assignment; use assignment or value-initialization instead

class should convert to pod type:
```
decimal12_t
uint24_t
doris::OLAPIndexFixedHeader
```


**Expected behavior**
no warning here


**Additional context**
Add any other context about the problem here.
