[libclc] [libclc] Use generic spirv*-unknown-unknown clang triple for SPIR-V targets (PR #199618)

[Nikita Popov via cfe-commits]

nikic wrote:

I don't care all that much what the triple is, just that we have a fixed one that is not going to change again in the LLVM 23 release cycle, so that it's actually possible to test this without things changing every other day.

Though I will say that the SPIRV-LLVM-Translator vs LLVM backend distinction should not be part of the triple in any case, that's supposed to be an implementation detail.

https://github.com/llvm/llvm-project/pull/199618