[llvm] [llvm-lit] Ignore malformed `.lit_test_times` entries (PR #191305)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

> When running llvm-lit, I sometimes hit a traceback, because a
.lit_test_times.txt file has got corrupted (not sure how).

It would be good to actually understand why.

Given the performance benefit is not super noticeable (10-15%) I feel silently ignoring malformed timing data could easily put us in a place where suddenly lit is actually outputting malformed timing data and no one notices. We should at least have a warning if we want to go down this direction.

https://github.com/llvm/llvm-project/pull/191305