[llvm] [AMDGPU] Add function attribute to disable TBUFFER combine (PR #156454)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

This is not a robust feature design, it is hacking out a singular transformation. You need to define a semantic meaning, have the default be conservatively correct

https://github.com/llvm/llvm-project/pull/156454