[llvm] [AMDGPU] Treat GEP offsets as signed in AMDGPUPromoteAlloca (PR #157682)

[Fabian Ritter via llvm-commits]

ritter-x2a wrote:

### Merge activity

* **Sep 10, 9:31 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/157682).


https://github.com/llvm/llvm-project/pull/157682