[clang] [Clang] Add `-fdefault-generic-addrspace` flag for targeting GPUs (PR #115777)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I agree in general that C/C++ has no semantic meaning ascribed to address spaces.

Err, C does. Please see TR 18037 (https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip)

AIUI, we've extended the C extension into C++, so we should be following the C semantics while mapping them on to C++'s stronger type system as closely as we can.

https://github.com/llvm/llvm-project/pull/115777