[llvm] [test] Fix `coro-split-dbg-labels.ll` for non-x86 (PR #147087)

[Adrian Vogelsgesang via llvm-commits]

vogelsgesang wrote:

This time around, the Linux and Windows pre-commit are actually green. I couldn't verify RISC-V and Sparc, since I don't have access to any such machines.

@rorth @asb Do you want to verify locally that this PR actually fixes the issue before I merge this? Or do you want me to land the patch as is? (hoping that it fixes the issue - in the worst case, it at least won't regress the current situation)

https://github.com/llvm/llvm-project/pull/147087