[llvm] [LoongArch] Support R_LARCH_{ADD, SUB}_ULEB128 for .uleb128 and force relocs when sym is not in section (PR #76433)

[WÁNG Xuěruì via llvm-commits]

xen0n wrote:

> > Hmm, I didn't see the reason for the zero-padding behavior as requested by @MaskRay in the commit [5f771fe](https://github.com/llvm/llvm-project/commit/5f771fee088f5029b278719f1a87b833a4492a14)?
> 
> The commit message has addressed that.

Ah, it's only explaining that zero-padding should be done on LoongArch. But I'm not sure if @MaskRay was asking for the reason behind the difference, i.e. the design considerations behind the decision.

https://github.com/llvm/llvm-project/pull/76433