[llvm] [AArch64] Consider runtime mode when deciding to use SVE for fixed-length vectors. (PR #96081)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

> I'm guessing there's another PR to change the scalable vector specific instances of hasSVEorSME()?

That's right. I didn't want to change everything in one big patch, but I'll follow this up afterwards.

https://github.com/llvm/llvm-project/pull/96081