[clang] [llvm] [clang][SPIR-V] Implement -fspv-preserve-interface (PR #196404)

[Diego Novillo via cfe-commits]

dnovillo wrote:

> SPIR-V changes look good to me. I'm not familiar with HLSL.

Thanks. @bogner would you be able to review the HLSL bits?

https://github.com/llvm/llvm-project/pull/196404