Switch to LLVM{Get,Set}CurrentDebugLocation2.

[eddyb]

I'm still not fully sure what's going on, but see llvm/llvm-project@cce4741.

We would probably have to polyfill it on versions that don't have those APIs.

[sanxiyn]

Enough time has passed that all supported versions (>=13) now have the change.

[workingjubilee]

Done in #109862