[clang] [clang][SPIR-V] Use the SPIR-V backend by default (PR #129545)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

LGTM, thanks! In what regards the translator use in the HIP Toolchain, from the AMD side we're looking at transitioning to the BE as soon as possible, but it will probably be some time until we have fully validated it.

https://github.com/llvm/llvm-project/pull/129545