[llvm] [lit] Add --report-failures-only option for lit test reports (PR #115439)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

The pre-merge code formatting check failed for the python code. You need to run `darker` on it to make sure it is formatted correctly.

LGTM, apart from that.

https://github.com/llvm/llvm-project/pull/115439