[llvm] [AArch64][SME] Fix accessing the emergency spill slot with hazard padding (PR #142190)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

Reduced godbolt case for the crash https://godbolt.org/z/eafscqW1c (using handwritten MIR as it's simpler, but the actual crash was found when marking a real benchmark function as streaming-compatible). 

https://github.com/llvm/llvm-project/pull/142190