[LoongArch] Ignore warnings when there is no environment in triple

In Rust bare-metal targets, there is no environment component in triple name. This patch ignores warnings that look like:

```
warning: triple-implied ABI conflicts with provided target-abi ‘lp64s', using target-abi
```

Reviewed By: SixWeining, xen0n

Differential Revision: https://reviews.llvm.org/D152778