[llvm] [llvm][llvm-lit] Add option to create unique result file names if results already exist (PR #112729)

[James Henderson via llvm-commits]

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

LGTM. Might want to wait for @pogo59 to confirm he's happy with this approach too.

https://github.com/llvm/llvm-project/pull/112729