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

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

> If the target doesn't have SVE, I don't think there is a need to save VG even in functions which have streaming-mode changes

Sure, but "-sve" doesn't mean the target doesn't have SVE; it just means the target may or may not has SVE.  What if you compile the code with SVE disabled, and the target actually does end up having SVE at runtime?  (e.g. you compile a library in SME-but-not-SVE mode, but it gets linked into an application that uses SVE.)

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