[clang] [clang][CodeGen] Add query for a target's flat address space (PR #95728)

[Matt Arsenault via cfe-commits]

arsenm wrote:

I still think we should not need this. DefaultIsPrivate is junk that needs to be deleted. Querying for LangAS::Default should always give the answer 0 for AMDGPU, which is what this is working around.

This clang notion of address space has nothing to do with your troubles with llvm.used in the IR or SPIRV 


https://github.com/llvm/llvm-project/pull/95728