[clang] [Clang][AArch64] Require SVE or SSVE for scalable types. (PR #91356)

[Paul Walker via cfe-commits]

https://github.com/paulwalker-arm requested changes to this pull request.

As discussed offline, I don't think we want to be this strict.  As demonstrated by the changes to the ACLE tests, this change makes it impossible to distribute a library in binary form that can work for both SVE and InStreamingMode environments.  I believe functions decorated with `__arm_streaming_compatible` should be allowed to assume the presence of the subset of instructions that is available to both environments. Library users get protected at the point they call such functions whereby a compilation error is emitted when the caller either doesn't have access to SVE or is not in streaming mode.

https://github.com/llvm/llvm-project/pull/91356