[libclc] [libclc] fix compiler check with --target=spirv64 and -disable-llvm-passes (PR #185376)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

Seems fine, targeting spirv64 should work without the backend with `-flto`.

https://github.com/llvm/llvm-project/pull/185376