[llvm] [WIP] [CodeGen] Enable TrapUnreachable by default for all targets. (PR #109732)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I think it would be more reasonable to change the default at -O0, and leave it as-is with optimizations enabled. If it's worth tracking down the marginal improvements you noticed, we could add an unreachable pseudo MachineInstr  

https://github.com/llvm/llvm-project/pull/109732