[clang] [lld] [llvm] [mlir] [IR] Introduce `T<address space>` to `DataLayout` to represent flat address space if a target supports it (PR #108786)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> > The LangRef doesn't need to know why it's undesirable. It's like the n field
> 
> `n` field? The following?
> 

Yes. It's an optimization hint 

https://github.com/llvm/llvm-project/pull/108786