[clang] Adding Loongarch64 to OpenBSD parts (PR #149737)

[Slava nerfur Voronzoff via cfe-commits]

nerfur wrote:

> Are you really working on Loongarch64 support?

Yes, I was trying to find some people to "sponsor" it (as much as I can do it as simple person), but decided that I can at least start, especially looking at experience of some freebsd guys (where I can start, what to add first, etc) 

I will check your other suggestions, thanks

https://github.com/llvm/llvm-project/pull/149737