[llvm] [AMDGPU] Add support for store to constant address space (PR #153835)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Is this a good idea? I think we should just report_fatal_error.

No, this should not be a fatal error. This is just undefined behavior that happens to be statically known. Treating it as invalid IR places a large burden on any pass that does some form of value propagation that makes an originally UB source obvious 

> Interestingly, @arsenm preferred to make it an IR verifier error in [788f94f](https://github.com/llvm/llvm-project/commit/788f94f731dc9ba514925ed0c5936c5e79f6abd8).

That's not an IR verifier error

https://github.com/llvm/llvm-project/pull/153835