[llvm] [LangRef] Require that vscale be a power of two (PR #145098)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

LGTM, but please wait a bit for more input.

It seems like not a lot of code actually depends on this, so if we have to walk back on this in the future due to new hardware, it shouldn't be too hard.

https://github.com/llvm/llvm-project/pull/145098