[llvm] [SystemZ] Add proper mcount handling (PR #135767)

[Dominik Steenken via llvm-commits]

dominik-steenken wrote:

The "Linux Premerge Checks" fail seems procedural rather than related to the PR:
```
Error: Failed to CreateArtifact: Received non-retryable error: Failed request: (409) Conflict: an artifact with this name already exists on the workflow run
```
How can i request a rebuild?

https://github.com/llvm/llvm-project/pull/135767