[libclc] [libclc] Remove bitcode prepare utility from OpenCL library build (PR #174447)

[Wenju He via cfe-commits]

wenju-he wrote:

spirv-llvm-translator translates LLVM IR to SPIR-V. It can also do reverse-translation.
llvm SPIR-V backend codegen output is SPIR-V, so there is no translation stage.
IIUC SPIR-V backend should provide native LLVM support while spirv-llvm-translator doesn't. There could be difference between how many llvm intrinsics that they can handle, but I don't know much as I haven't worked on the SPIR-V backend.
SYCL compiler used to use spirv-llvm-translator, but recently has been switching to the SPIR-V backend.

https://github.com/llvm/llvm-project/pull/174447