[llvm] [AArch64] Fix SVE callee-save layout for nounwind functions on Windows (PR #156467)

[Eli Friedman via llvm-commits]

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

I think in practice needsWinCFI will almost always be true on Windows; clang will add "uwtable" attributes.

In order to reduce the number of different configurations, I think I'd prefer to always use Windows-style prologue/epilogue lowering on Windows, even if it isn't strictly required.

https://github.com/llvm/llvm-project/pull/156467