[clang] [Clang][CodeGen] Start migrating away from assuming the Default AS is 0 (PR #88182)

[Jessica Clarke via cfe-commits]

jrtc27 wrote:

> querying a modules default AS from the target, rather than assuming it's 0

I do think this should likely be part of the DataLayout. We have defaults for globals, alloca and functions, but no generic "give me the address space for `void *`"-like thing in LLVM itself.

https://github.com/llvm/llvm-project/pull/88182