[llvm] [ci] Don't add more check targets if "check-all" is present (PR #110277)

[David Spickett via llvm-commits]

DavidSpickett wrote:

As much as I would prefer `check-all` because it prints one set of results, we can't do that for all builds so I'll fix that some other way.

> Oh, nice! I think we can skip over adding even more logic into the bash script that generates the pipeline. I wonder if pstl and libclc can get the same treatment.

There is no `check-libclc` target at the moment. It has a tests folder and cmake calls `enable_testing` but I couldn't find out how to run any of them. I wonder if it's not worth running anything if you don't know you have a specific GPU installed.

We can use `check-pstl` for pstl but when I tried it it just immediately failed to compile, which isn't unexpected but also I couldn't find any instructions or public builds to copy from.

`check-all` in the same build did not fail, so I suspect that pstl tests are not being run in `check-all` anyway.

If I can prove that:
* Doing anything with libclc is pointless if there's no gpu to run it on
* Pstl isn't being tested by `check-all` anyway

Then we can use `check-compiler-rt` and just add nothing extra for libclc and pstl.

https://github.com/llvm/llvm-project/pull/110277