[llvm] [AArch64] Reject non-scalable types in named Z-register constraints (PR #217551)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

@Stylie777 - The type legality observations are all existing issues? Rightly but more likely wrongly, the current implementation assumes C usage and thus relies on the known legal types.  I'm not 100% sure but I suspect using C inline asm to set `svint8x2_t` likely variables may well fail before we get this far.  Either way, it feels like a separate and larger issue than the one this PR is trying to fix?

https://github.com/llvm/llvm-project/pull/217551