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

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

Instead of forcing a base pointer, we could relocate the emergency spill slot so it's part of the callee-save region.  But I guess if you do that's, it's expensive to refer to local variables, even if it's still technically possible.  Not sure.  Having two variable-sized regions on the stack makes the stack layout complicated.

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