[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:

> Just to clarify, does this mean any two non-flat address space pointers _cannot_ alias?

This should change nothing about aliasing. The IR assumption is any address space may alias any other 

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