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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Really, there is no need for a mesa specific triple and there will most likely never be one. And I'm getting tired of explaining it over and over again, so please don't make this more difficult than it needs to be.

Sorry, don't mean to be a nuisance, but I'm trying to figure out how this is intended to be used in Mesa. We very recently overhauled the `libclc` build artifacts and I just want to make sure I'm up  to speed. My understanding is that the old build emitted this as the following with **mesa3d** in the name.
```
clc/spirv64-mesa3d-.spv
```
The changes now cause it to be emitted in a per-triple directory (as is standard in LLVM/Clang handling now)
```
spirv64-unknown-unknown/libclc.spv
or
spirv64-mesa-mesa3d/libclc.spv
```

My question is whether or not dropping the `mesa3d` reference is intentional. I did a quick search of the Mesa sources and they seem to reference **mesa3d** as well, so what am I missing? My understanding is that the objection is moving it form the name to the triple?
https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/compiler/clc/nir_load_libclc.c#L44

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