Handle new `caller_location` intrinsic the right way

[adpaco]

Rebase from #346 found a new caller_location intrinsic in the process. In order to unblock, we codegen this intrinsic as:

            "caller_location" => {
                codegen_unimplemented_intrinsic!("https://github.com/model-checking/rmc/issues/374")
            }

But we can probably codegen it the same way Rust does.

[celinval]

This is a nice explanation on what this does: https://hegdenu.net/posts/track-caller/