[llvm] [JITLink][LoongArch] Add R_LARCH_{B16, B21} relocations support (PR #121096)

[via llvm-commits]

zhaoqi5 wrote:

> FYI, this uncovered a problem on 32-bit hosts which I fixed in [5cf138c](https://github.com/llvm/llvm-project/commit/5cf138cfbaa8040100fed1d0d5e0a189759b24ab).

I once considered whether using `UL` here might cause issues, but overlooked testing on 32-bit platform. Thank you for fixing it.

https://github.com/llvm/llvm-project/pull/121096