Include repo name in merge commit message?

[RalfJung]

Both Clippy and Miri use some sort of tooling to reflect their own local history into the rustc repo, preserving individual commits. This unfortunately means that when bors creates a Miri merge commit like "Auto merge of #2636 - RalfJung:scalar-field-retag, r=oli-obk", when that commit gets put into the rustc repo, Github interprets #2636 as a rustc PR number, which of course leads to bogus links.

Would it be possible for bors to create these commit messages in a way that the links will keep working when the message is put into a different repo, at least within the rust-lang org?