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

[Steven Perron via llvm-commits]

https://github.com/s-perron approved this pull request.

I don't see any problem, but I'm not familiar with standard practices in llvm. I like having the combiner pass.

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