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

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> This is something you need to handle in the SPIRV backend. This type information will cease to exist in the future.

What do you mean by `This type information will cease to exist in the future`? Is there a plan to remove the type operand from the GEP instruction?

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