[clang] [llvm] [Offload] Add support for loongarch64 to host plugin (PR #120173)

[via llvm-commits]

wangleiat wrote:

> Does this actually work?

I executed the `ninja check-offload` command on `LoongArch64`, and the results are as follows:

Befor [commit](https://github.com/llvm/llvm-project/pull/120173/commits/7edfb3eb052643ebe2f4bc750cd96d980f782a84): 
```         
Total Discovered Tests: 658
Unsupported: 320 (48.63%)  
Passed     :  30 (4.56%)   
Failed     : 308 (46.81%)  
```                           
After:
```          
Total Discovered Tests: 658
Unsupported: 320 (48.63%)  
Passed     : 296 (44.98%)  
Failed     :  42 (6.38%)   
```

https://github.com/llvm/llvm-project/pull/120173