[llvm] [RemoveDIs] Fix SIGSEGV caused by splitBasicBlock (PR #90312)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Looks correct at a surface level; I'm out-of-office for a while though, Stephen/Orlando should be able to confirm this is a good fix.

https://github.com/llvm/llvm-project/pull/90312