[llvm] Clarify conditions of `lit` exiting with exit code 1 (PR #136190)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

I'm not sure `--report-failures-only` should be considered a canonical reference of what is considered a "failure" any more than the list you've provided here is. More generally, I don't think it's useful to attempt to specify a comprehensive list of failure kinds, as it could easily rot, if somebody extended the set of failures with a new variety.

How about "... an exit code of 1, if there are any failure results, for example FAIL or XPASS results. Otherwise, it will ..."?

https://github.com/llvm/llvm-project/pull/136190