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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Thanks, looks good.

Personally, I don't really have a preference one way or the other, but I'm curious why the mesa version wasn't desired. The normal way that would've worked is it would control the toolchain such that you could just do `clang --target=spirv64-mesa-mesa3d` and the compiler would know how to give you a functional artifact. I don't know how the mesa project chooses to build their shaders though.

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