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

[Louis Dionne via llvm-commits]

ldionne wrote:

> 
> Sure. I mean a dedicated target to run compiler-rt tests, like we have `check-clang` or `check-cxx` for Clang and libc++ tests respectively.

Ah, thanks! There's already a `check-compiler-rt` target defined by compiler-rt, so I'm kinda surprised we're not just calling that. I guess that's what you meant.

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