[llvm] Revert "[SimplifyCFG] Deduce paths unreachable if they cause div/rem UB" (PR #137741)

[Bill Wendling via llvm-commits]

bwendling wrote:

> > Whether we generate a __builtin_trap or simply allow the calculation to happen is fine by me, but what we shouldn't do is generate broken code simply because it's UB.
> 
> Is `--trap-unreachable` helpful for your case? TBH it is still unreliable since the optimizer may remove the whole BB and turn a conditional branch into an unconditional one.

It helps some, but causes other issues. From the Linux objtool:

```
panic() missing __noreturn in .c/.h or NORETURN() in noreturns.h
```

https://github.com/llvm/llvm-project/pull/137741