[clang] [llvm] [SPIRV] add pre legalization instruction combine (PR #122839)

[Vyacheslav Levytskyy via llvm-commits]

VyacheslavLevytskyy wrote:

> > I see also some problems in test cases
> 
> @VyacheslavLevytskyy the SPIRV test case failures are not related to my change. They are also failing on main.

I will check now. For one the reason is clear, https://github.com/llvm/llvm-project/pull/123191

https://github.com/llvm/llvm-project/pull/122839