[llvm] [PowerPC] Spill non-volatile registers required for traceback table (PR #71115)

[Maryam Moghadas via llvm-commits]

maryammo wrote:

> > I missed your ping, sorry Zheng.
> 
> No worries at all. Thanks very much for working on this.
> 
> I still confused by the `nounwind` attribute changes. I thought you were adding this attribute to suppress some CFI instructions. But I tested this patch locally, without this attribute changes, all the impacted LITs are still good. So I don't think we need the `nounwind` attribute change, right? The CSR should always backup/restore till 31 without considering the nounwind attribute?

You are right, that is not needed. Thanks. 

https://github.com/llvm/llvm-project/pull/71115