[clang] [AArch64][SME] Warn when using a streaming builtin from a non-streaming function (PR #75487)

[Sander de Smalen via cfe-commits]

https://github.com/sdesmalen-arm approved this pull request.

Assuming the tests pass after changing `BuiltinType` to a `std::optional`, the patch looks fine to me.

https://github.com/llvm/llvm-project/pull/75487