[llvm] [BasicBlockUtils] Fix loopinfo header in split block before (PR #179408)

[Yevgeny Rouban via llvm-commits]

yrouban wrote:

> In that case, can you please rebase this to leave just the new test?

ok, but when #179392 is landed. Or it could be 2 patches: before and after #179392. The first one is crashing in DEBUG mode, the second is paasing due to #179392.

Another choice is to incorporate the testcase into #179392 as I suggested there.


https://github.com/llvm/llvm-project/pull/179408