Cannot boot Nim on Loongarch64
### Description

Loongarch64 linux support was once added, but currently I'm trying to compile Nim on it but it failed on `csource_v2`'s build.

### Nim Version

2.1.99 (source code)

### Current Output

```text
Error: no C code generated for: [Linux: Loongarch64]
```


### Expected Output

```text
(compile)
```


### Known Workarounds

After a large time of search and exploring, I've finally make a built Nim on Loongarch64, but in a very ungraceful way:


As loongarch64 is always little endianess, and it used to be mips compatible.

I tried to manually modify csources_v2/makefile  (of course later I found this file is generated by tools/niminst/makefile.nimf, and that's why I report issue here instead of csources_v2 repo)

and copied mips64el's build code for loongarch64.

In this way Nim compiles.

### Additional Information

One thing to note is that maybe due to my mistake when manual modifying, the built Nim's configure rrally becomes as if on mips64el...


I've run `kock test` locally in this Loongarch64 mechine, and it only failed 3 tests currently.

(at least one of them is due to the problem mentioned above)