[PATCH] D41776: [lit] Implement "-r" option for builtin "diff" command + a test using that.

[Max Moroz via Phabricator via llvm-commits]

Dor1s added a comment.

1. For some reason, it appears to be important to use `stdout.write` instead of `print`, so replacing these.

2. Commands implemented in `TestRunner.py` can't be used as part of a pipeline, this is why there are several `diff-error-*` tests. I don't see a better way to test negative scenarios rather than split my test into `diff-r-error-*` and check their output in `shtest-shell.py` as it's done for existing tests


https://reviews.llvm.org/D41776