[llvm] [AArch64][SME] Save VG for unwind info when changing streaming-mode (PR #83301)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

If the ABI spec is intentionally not supporting the combination for now, that's fine, I guess?  As you note, it should be feasible to extend the ABI without breaking backward-compatibility.  Probably the compiler should report an error on the unsupported combinations, though.

https://github.com/llvm/llvm-project/pull/83301