[llvm] [AMDGPU] Pre-commit tests for "lshr + mad" fold (PR #119509)

[Vikram Hegde via llvm-commits]

vikramRH wrote:

gentle ping. apologies for the short frequency, I'm hoping to at least get some inputs on the main PR before the holidays :)

https://github.com/llvm/llvm-project/pull/119509