[compiler-rt] [AArch64][SME] Rewrite __arm_get_current_vg to preserve required registers (PR #100143)

[Kerry McLaughlin via llvm-commits]

kmclaughlin-arm wrote:

> Should this be backported to 19.x

Hi @AtariDreams, yes it should be. I will create an issue to backport it.

https://github.com/llvm/llvm-project/pull/100143