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

[via llvm-commits]

maryammo wrote:

The failure reported above is` CodeGen/PowerPC/ldst-16-byte-asm.mir` which is fix by https://github.com/llvm/llvm-project/pull/70758. So this  patch depends on  https://github.com/llvm/llvm-project/pull/70758.

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