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

[Christian Sigg via llvm-commits]

chsigg wrote:

> > always emitting ISD::TRAP as `trap; exit;`
> 
> That would be fine.

Ok, I changed it to that. It seems a little cleaner because it a) avoids `trap; exit; trap;` and b) conveys to `ptxas` that `trap`s from intrinsics exit the CFG as well.

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