[llvm] [InstCombine] Prevent i8 canonicalize for SPIR-V (PR #147527)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> Yes, the type operand will be removed as part of https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699.
> 
> I brought this up as a potential concern when the SPIRV target was promoted to non-experimental (https://discourse.llvm.org/t/rfc-promoting-spir-v-to-an-official-target/83614) and maintainers were confident that they will be able to accommodate this change in the SPIRV backend.

Ahh thanks! Well, looks like I should get started then.. thanks!

https://github.com/llvm/llvm-project/pull/147527