Revert "Stop git from merging generated files" This reverts https://github.com/rust-lang/rust/pull/133851. "-merge" makes git not even do merges if they are entirely conflict-free, which is not the behavior we want. We sometimes have conflict-free merges in generated files and it's much better if git can handle them automatically. r? `@oli-obk` Cc `@jieyouxu` `@Urgau`