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

[Evgenii Kudriashov via llvm-commits]

e-kud wrote:

@RemiSEGARD Thanks! Let me check some tests where I've seen fallback due to  `G_BRJT`.
Tagging @turinevgeny as he may have some related work.

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