[llvm] [SPIR-V] Change a way SPIR-V Backend API works with user facing options (PR #124745)

[Vyacheslav Levytskyy via llvm-commits]

VyacheslavLevytskyy wrote:

@nikic Are we good to merge or you'd like to proceed with the review?

https://github.com/llvm/llvm-project/pull/124745