[llvm] [X86][GlobalISel] Enable G_BRJT (PR #81811)

[Rémi SEGARD via llvm-commits]

RemiSEGARD wrote:

@e-kud Sorry for the late reply, I haven't had much time recently. I applied your suggestions.

I also noticed that when compiling your example with `-m32` the legalization of `G_BRJT` fails because `MJTI->getEntryKind()` returns `EK_Custom32` which seems to be using a global offset table. I haven't had time to look into how to handle that for now. If you have some tips on where to look it would be much appreciated!

https://github.com/llvm/llvm-project/pull/81811