[llvm] [CodeGen] Make LoadExtActions address-space aware (PR #162407)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

> OR: We change the tactic a little. Make the map an optional override. 

All targets should use a uniform interface. If you add a special upgrade path, no targets will move to use it in the next 5+ years. Don't shy away from making changes to every backend, we have a lot of stalled "targets can upgrade to this some day" APIs but that hardly ever happens in practice 

https://github.com/llvm/llvm-project/pull/162407