[clang] [llvm] [HLSL] Add initial support for output semantics (PR #168095)

[Nathan Gauër via cfe-commits]

Keenuts wrote:

This PR broke some buildbots, just a missing include. Sending https://github.com/llvm/llvm-project/pull/168739 to fix forward.

https://github.com/llvm/llvm-project/pull/168095