[llvm] [DAGCombiner][AMDGPU] Track signedness in ByteProviders (PR #65995)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

Sorry for the immediate ping, however it, as it stands, the dot4 combine is causing failures which are blocking integration with upstream. I will either need to upstream this quickly or revert the commit and patch it offline.

https://github.com/llvm/llvm-project/pull/65995