[libclc] [libclc] Canonicalize 'clspv' to the 'spirv-unknown-vulkan' triple (PR #196351)

[Romaric Jodin via cfe-commits]

rjodinchr wrote:

Adding `spirv32` everywhere we have `spirv64` and targeting `spirv32-unknown-vulkan` works fine for `clspv`.

https://github.com/llvm/llvm-project/pull/196351