[llvm] [SPIRV] Sign-extend operands of sign-sensitive ops on sub-pow2 widths (PR #203661)

[Dmitry Sidorov via llvm-commits]

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

Please add a regression test for the miscompile I've showed on the previous review iteration.

There is one inefficiency in the compiled code, but not a miscompile/not a blocker, feel free to add as TODO.

But overall LGTM.

https://github.com/llvm/llvm-project/pull/203661