[llvm] Remove `br i1 undef` from regression tests (PR #115130)

[Nuno Lopes via llvm-commits]

nunoplopes wrote:

> The changes in the DebugInfo directory look good.
> 
> I get the feeling that earlydup-crash.ll is the most likely to accidentally lose some tests coverage, as it's a crash-test with a broad input that (potentially) generates substantially different code for well-defined branches rather than undef branches. However, given that IIRC undef branches will eventually not be supported by LLVM, this is unavoidable.

ok, then we can leave that test with `br poison` instead, so it gets out of the conversion queue, while keeping the coverage.

https://github.com/llvm/llvm-project/pull/115130