[llvm] [NVPTX] Fix code generation for `trap-unreachable`. (PR #67478)

[Tim Besard via llvm-commits]

https://github.com/maleadt approved this pull request.

LGTM.

It didn't occur to me to preserve the `trap` as in Julia we're mostly avoiding that instruction since it 'breaks' the GPU for the current process, without a way to reset.

https://github.com/llvm/llvm-project/pull/67478