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

[Shilei Tian via llvm-commits]

shiltian wrote:

> Yes, this is more like module-level property. But function attribute is a standard way to pass this kind of information from the front-end to the backend. Is there a better option?

If this is a module level thingy, please just use module flag. We already have something "bad" that is supposed to be a module-level config but ends up being a function level attribute, which causes many trouble.

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