[clang] [HIP] Don't add -fvisibility=hidden for SPIR-V compilation flow (PR #184821)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 commented:

SPIR-V may not have the concept of visibility, but LLVM-IR does. If you don't emit hidden visibility you're probably going to kill any hopes of internalizing functions through LLVM's LTO pass.

https://github.com/llvm/llvm-project/pull/184821