[llvm] [LoongArch] Emit R_LARCH_RELAX when expanding some macros (PR #120067)

[via llvm-commits]

zhaoqi5 wrote:

> This looks quite simple, except for one question: for macro instructions that can be relaxed, do we unconditionally add the `R_LARCH_RELAX` relocation?

I think it is ok, as long as the macro instruction can be relaxed, we can attach the `R_LARCH_RELAX` relocation to the emitted code sequence to try to perform linker relaxation.

https://github.com/llvm/llvm-project/pull/120067