[clang] [libc] [llvm] [libc] Add support to build and run libc tests with spirv backend (PR #208129)

[via cfe-commits]

fineg74 wrote:

> Does the `llvm-gpu-loader` work on SPIR-V now?

With the changes in this PR it does work on SPIR-V 

https://github.com/llvm/llvm-project/pull/208129