[llvm] [Aarch64] [ISel] Don't save vaargs registers if vaargs are unused (PR #126780)

[Hans Wennborg via llvm-commits]

zmodem wrote:

> Is there any way to reproduce these results locally? At least to understand what got broken and try to fix it

I don't have a great setup for debugging win/arm64 right now. Maybe the Linaro folks have a better idea of what's happening.

I think I could share the binary that's failing though, in case that's useful.

https://github.com/llvm/llvm-project/pull/126780